Code files (with a .cpp extension) are not the only files commonly seen in programs. The other type of file is called a header file, sometimes known as an include file. Header files almost always have a .h extension. The purpose of a header file is to hold declarations for other files to use.
Using standard library header files
Consider the following program:
#include <iostream>
int main()
{
using namespace std;
cout << "Hello, world!" << endl;
return 0;
}
This program prints “Hello, world!” to the console using cout. However, our program never defines cout, so how does the compiler know what cout is? The answer is that cout has been declared in a header file called “iostream”. When we use the line #include <iostream>, we are telling the compiler to locate and then read all the declarations from a header file named “iostream”.
Keep in mind that header files typically only contain declarations. They do not define how something is implemented, and you already know that your program won’t link if it can’t find the implementation of something you use. So if cout is only defined in the “iostream” header file, where is it actually implemented? It is implemented in the runtime support library, which is automatically linked into your program during the link phase.
A library is a package of code that is meant to be reused in many programs. Typically, a library includes a header file that contains declarations for everything the library wishes to expose (make public) to users, and a precompiled object that contains all of the implementation code compiled into machine language. These libraries typically have a .lib or .dll extension on Windows, and a .a or .so extension on Unix. Why are libraries precompiled? First, since libraries rarely change, they do not need to be recompiled often, if ever. It would be a waste of time to compile them every time you wrote a program that used them. Second, because precompiled objects are in machine language, it prevents people from accessing or changing the source code, which is important to businesses or people who don’t want to make their source code available for intellectual property reasons.
Writing your own header files
Now let’s go back to the example we were discussing in the previous lesson. When we left off, we had two files, add.cpp and main.cpp, that looked like this:
add.cpp:
int add(int x, int y)
{
return x + y;
}
main.cpp:
#include <iostream>
int add(int x, int y); // forward declaration using function prototype
int main()
{
using namespace std;
cout << "The sum of 3 and 4 is " << add(3, 4) << endl;
return 0;
}
We’d used a forward declaration so that the compiler would know what add was when compiling main.cpp. As previously mentioned, writing forward declarations for every function you want to use that lives in another file can get tedious quickly.
Header files can relieve us of this burden. A header file only has to be written once, and it can be included in as many files as needed. This also helps with maintenance by minimizing the number of changes that need to be made if a function prototype ever changes (eg. by adding a new parameter).
Writing our own header files is surprisingly easy. Header files consist of two parts. The first part is called a header guard, which is discussed in the next lesson (on the preprocessor). The second part is the actual content of the .h file, which should be the declarations for all of the functions we want other files to be able to see. Our header files should all have a .h extension, so we’ll call our new header file add.h:
add.h:
#ifndef ADD_H #define ADD_H int add(int x, int y); // function prototype for add.h #endif
In order to use this header file in main.cpp, we have to include it. Here is the new main.cpp:
main.cpp that includes add.h:
#include <iostream>
#include "add.h" // this brings in the declaration for add()
int main()
{
using namespace std;
cout << "The sum of 3 and 4 is " << add(3, 4) << endl;
return 0;
}
When the compiler compiles the #include "add.h" line, it copies the contents of add.h into the current file. Because our add.h contains a function prototype for add(), this prototype is now being used as a forward declaration of add()!
Consequently, our program will compile and link correctly.
You’re probably curious why we use angled brackets for iostream, and double quotes for add.h. The answer is that angled brackets are used to tell the compiler that we are including a header file that was included with the compiler. The double-quotes tell the compiler that this is a header file we are supplying, which causes it to look for that header file in the current directory containing our source code first.
Rule: Use angled brackets to include header files that come with the compiler. Use double quotes to include any other header files.
Another commonly asked question is “why doesn’t iostream have a .h extension?”. The answer is, because iostream.h is a different header file than iostream is! To explain requires a very short history lesson.
When C++ was first created, all of the files in the standard runtime library ended in .h. Life was consistent, and it was good. The original version of cout and cin lived in iostream.h. When the language was standardized by the ANSI committee, they decided to move all of the functions in the runtime library into the std namespace (which is generally a good idea). However, this presented a problem: if they moved all the functions into the std namespace, none of the old programs would work any more!
To try to get around this issue and provide backwards compatibility for older programs, a new set of header files was introduced that use the same names but lack the .h extension. These new header files have all their functionality inside the std namespace. This way, older programs that include #include <iosteam.h> do not need to be rewritten, and newer programs can #include <iostream>.
Make sure when you include a header file from the standard library that you use the non .h version if it exists. Otherwise you will be using a deprecated version of the header that is no longer supported.
As a side note, many headers in the standard library do not have a non .h version, only a .h version. For these files, it is fine to include the .h version. Many of these libraries are backwards compatible with standard C programming, and C does not support namespaces. Consequently, the functionality of these libraries will not be accessed through the std namespace. Also, when you write your own header files, they will all have a .h extension, since you will not be putting your code in the std namespace.
Rule: use the non .h version of a library if it exists, and access the functionality through the std namespace. If the non .h version does not exist, or you are creating your own headers, use the .h version
Header file best practices
Here are a few best practices for creating your own header files.
- Always include header guards.
- Do not declare variables in header files unless they are constants. Header files should generally only be used for declarations.
- Do not define functions in header files unless they are trivial. Doing so makes your header files harder for humans to read.
- Each header file should have a specific job, and be as independent as possible. For example, you might put all your declarations related to functionality A in A.h and all your declarations related to functionality B in B.h. That way if you only care about A later, you can just include A.h and not get any of the stuff related to B.
- Try to include as few other header files as possible in your header files.
 1.10 — A first look at the preprocessor
|
 Index
|
 1.8 — Programs with multiple files
|
[...] 2007 Prev/Next Posts « 1.7 — Forward declarations | Home | 1.9 — Header files » Saturday, June 2nd, 2007 at 8:26 [...]
[...] the lesson on header files, you learned that you can put functions inside header files in order to reuse them in multiple [...]
Ok I have an issue here with the headers. I deviated from the last lesson slighy but it is close to the same. Please tell me where I went wrong with Header Files.
Here is Program1.cpp
// Program1.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include #include "MATH.h" int main() { using namespace std; int a = 0; int b = 0; cout > a; cout > b; cout And here is MATH.cpp#ifndef MATH_H #define MATH_H int Multiply(int x, int y) { using namespace std; return x * y; } int Add(int x, int y) { using namespace std; return x + y; } int Subtract(int x, int y) { using namespace std; return x - y; } #endifHere is my output from VS2008:
1>------ Build started: Project: Program1, Configuration: Debug Win32 ------
1>Compiling...
1>Program1.cpp
1>c:\documents and settings\jstuart\my documents\visual studio 2008\projects\program1\program1\program1.cpp(18) : error C3861: 'Multiply': identifier not found
1>c:\documents and settings\jstuart\my documents\visual studio 2008\projects\program1\program1\program1.cpp(19) : error C3861: 'Add': identifier not found
1>c:\documents and settings\jstuart\my documents\visual studio 2008\projects\program1\program1\program1.cpp(20) : error C3861: 'Subtract': identifier not found
1>MATH.cpp
1>c:\documents and settings\jstuart\my documents\visual studio 2008\projects\program1\program1\math.cpp(28) : fatal error C1010: unexpected end of file while looking for precompiled header. Did you forget to add '#include "stdafx.h"' to your source?
1>Generating Code...
1>Build log was saved at "file://c:\Documents and Settings\jstuart\My Documents\Visual Studio 2008\Projects\Program1\Program1\Debug\BuildLog.htm"
1>Program1 - 4 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
The problem might be that you named your math.h file math.cpp. Try renaming your math.cpp to math.h and see if it fixes your issue. If that doesn’t work, try reposting your problem in the forum. The forums don’t have any many problems with posted programs as wordpress seems to.
Spot on that worked. I changed MATH.cpp to Math.h and it worked fine. Thanks for the tutorial and the response Alex.
First of all thank you Alex for the excellent tutorials.
a questions please:
from jestuart’s code; I thought he will at least need three files, one for the header, one for the actual function and then one for main e.g
Math.h – which contains the forward declaration
Math.cpp – which will contain the actual function definition
main.cpp – which will reference the .h files
here is my code for a similar operation; using code::block
main.cpp
#include <iostream>
#include "math.h"
int main()
{
using namespace std;
cout << "3 + 4 = " << add(3, 4) << endl;
cout << "3 – 4 = " << sub(3, 4) << endl;
cout << "3 * 4 = " << multiply(3, 4) << endl;
return 0;
}
math.cpp
int add( int x, int y)
{
return x + y;
}
int sub(int x, int y)
{
return x – y;
}
int multiply(int x, int y)
{
return x * y;
}
math.h
#ifndef MATH_H
#define MATH_H
int add(int x, int y);
int sub(int x, int y);
int multiply(int x, int y);
#endif
thank you abdul for the code. i tried to run the code above, i am using codeblocks in Windows 7, but kept getting an error that says as follows:
“undefined reference to `add(int, int)’
“undefined reference to `sub(int, int)’
“undefined reference to `multiply(int, int)’
however, i was able to resolve this issue by adding this line of code
inside the header file or the math.h file
the following is the final code for the header (math.h) file:
thank you for the nice tutorials everyone! :)
[...] Header files [...]
Hmm, first of all great job with the tutorials. I have finally decided to familiarize myself with C++ and I really like it so far, however I’m a bit confused with this and have a question.
So my question is the following: Should be include the header file for every source file (in this case I’m thinking about add.cpp or can we only use it for one source file. Also, isn’t it going to scream at us for “redefining?” the functions?
Edit: I just found out. The header guard prevent that from happenning. As for using it in all the source files makes it easier and saves times?
Excuse my english, it is not my native tongue. :P
As you’ve noted, the header guards prevent the header files from being included multiple times. It’s a sloppy way of doing things, in my opinion, but it works and it’s the standard way to do it.
Ideally, you should include your header file in every .cpp file in which you use the stuff it declares. However, in practice, since header files can include other header files, this may not be strictly necessary. For example, you might have a class named Foo that uses strings, so foo.h will include string.h. foo.cpp (which also uses strings) should ideally include both foo.h and string.h, but since foo.h already includes string.h, if you only include foo.h you will still be able to use strings.
[...] 2007 Prev/Next Posts « 1.9 — Header files | Home | 1.11 — Comprehensive quiz » Sunday, June 3rd, 2007 at 12:57 [...]
I use Bloodshed Dev-C++ and i keep geting these error messages while trying to compile:
C:Dev-CppMakefile.win [Build Error] [Project1.exe] Error 1
ld returned 1 exit status
[Linker error] undefined reference to `add(int, int)’
I copied the add header and saved it as a .h file in the same directory as the project. Has anyone else had this error? How can I fix it?
Nevermind, I got it to work by changing the header from:
add(int x, int y)
to:
add(int x, int y)
{ return x + y: }
Had same problem as Chase. his solution worked for me also. Thanks Chase
I had the same problem also and chases worked. and i see the following post by TBM clarifying you should have 3 parts. main.cpp, add.cpp and the add.h but this is not clear to me and others above me from the tutorial.
By the way I would like to add this is by far an amazing tutorial and I have learned alot being new.
Thank you very much.
Best Regards
The problem Chase had here as do to the omission of the semi colon ” ; ” after his prototype for his header file and the reason it was fixed when he changed it was simply do to the fact that he defined it within the header itself instead of in a separate .cpp file.
In other words his declaration should have looked like this in his header file:
add(int x, int y); <— notice the semi colon.
When changed to:
add(int x, int y)
{
return x + y;
}
It was no longer a prototype but a definition, meaning that the add.cpp file was no longer needed do to the fact that the definition is also now held in the header file. At least this is my understanding so far.
Oh, and yes I know his change uses a colon instead of a semi colon, I’m just guessing that it was a typo.
I had this problem too and couldn’t understand what was being wrong (I was trying out the IDE Geany).
Until I realised that Geany didn’t compile both of the two .cpp files, and link them together.
When I manually compiled/linked them with g++ it worked just fine.
Another interesting part of the tutorial. I learnt a lot about namespaces here. Thanks again for the great tutorial
This is a great tutorial. Thanks for the time that you put into it.
I’ve got a question: I’m working on a dialog in a solution (in VS 2005) that contains several projects. I’m trying to access one of the classes from another project, but I keep getting a linking error. I have done a #include “headerfile.h” and have added the path to my “Additional include directories” in the properties pages via the IDE. I’m unable to copy the .h file into my local directory, because it references a resource.h file located in it’s project. My dialog has a resource.h file of its own. Has anyone had a similar problem?
Generally you’ll get a linker error when you include all the appropriate header files but don’t include the actual definition of what’s in the header files. I’m guessing you need to include some of the .cpp files from the other project in the project you’re getting the linker error for.
i used the codes that you posted in the tuturial which are
#ifndef ADD_H
#define ADD_H
int add(int x, int y); // function prototype for add.h
#endif
and in the other file
#include <iostream>
#include "add.h" // this brings in the declaration for add()
int main()
{
using namespace std;
cout << "The sum of 3 and 4 is " << add(3, 4) << endl;
return 0;
}
and since im using visual C++ 2008 i added #include "stdafx.h" to the top of the code but it always comes up with these errors
1>—— Build started: Project: hmmm, Configuration: Debug Win32 ——
1>Compiling…
1>hmmm.cpp
1>c:\my documents\visual studio 2008\projects\hmmm\hmmm\hmmm.cpp(3) : fatal error C1083: Cannot open include file: ‘add.h’: No such file or directory
1>Build log was saved at “file://c:\My Documents\Visual Studio 2008\Projects\hmmm\hmmm\Debug\BuildLog.htm”
1>hmmm – 1 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
i have no clue what im doing wrong =/
BTW so far the tuturials have been pretty good so thanks for taking your time to write it all
sorry i put the code in brackets like it says but they somehow got deleted when i posted it
The only thing I can think of is that maybe you didn’t save add.h into the correct directory?
I had the same problem till I realised that of course files are saved to the last place used so VS was saving to the mutli file project from the prior lesson. moved the .h file to the folder for this project and its ok
Hello Alex,
First of all I would like to thank you very much for taking time and posting such a wonderful tutorial. You have mentioned namespaces, but coming from ‘C’ programming background, I never came across ‘namspaces’. Can you please explain the basics and what these namespaces are? Thank you once again.
Kkamudu
I cover that topic in lesson 7.11 on namespaces. Even though it’s in chapter 7, any readers who are curious might have a look now — I think it will be pretty comprehensible even with just the knowledge presented in chapter 1.
In the actual add.cpp return (x + y) was stored.
In add.h this sentence is not part of the code. How does the compiler/linker know that the sum of
x + y is needed as the result?
Niels
When main.cpp #includes add.h, the function prototype for add() is imported into main.cpp. The compiler uses this add() prototype to ensure anyone calling add() is doing so correctly.
Once the compiler is satisfied no syntax or type-checking errors exist, the linker takes over. The linker’s job is to combine all of the individual .cpp files into a single unit (generally an executable or DLL), and ensure that all of the function calls resolve to an actual defined function.
If you forgot to include add.cpp in your project, your project would still compile okay (because the compiler could use the prototype to do type checking), but it would fail in the linker stage because the linker would be unable to resolve the call to add() to a specific function.
Thanks Alex! I had this doubt while reading the tutorial. Greatly explained.
Foremost, thanks a ton for such a wonderful tutorial.
Thanks for this tutorial, I have a question:
I the second graphic, you showed the work of the compiler and linker with source files,
Why there is not an arrow from add.cpp to add.h, since add.h is only declaration
(which include function prototypes and variables) that add.cpp implemented?
Thank you,
Add.h would be brought in under both add.cpp and main.cpp since they both include it. I didn’t show it being brought in under add.cpp for space consideration reasons.
Hey,
Thoroughly enjoying this tutorial too! Also the best I’ve seen so far online.
I’m having some trouble compiling too!! I’m using a Cygwin bash shell
I have 3 programs:
The first is main.cc:
#include <iostream> #include "add.h" int main() { using namespace std; cout << "The sum of 3 and 4 is: " << add(3, 4) << endl; return 0; }The next is add.cc
int add(int x, int y) { return x + y; }and lastly I have add.h
All files are contained in the same folder that I have been using for all my other programs.
I have been compiling previous programs using c++ filename.cc -o filename.exe
The error message I get reads:
“MYFOLDER/cc9iZFXR.0:main.cc(.text+0x13b): undefined reference to ‘add(int,int)’
collect2: Id returned 1 exit status
****************
If you can provide any advice here it would be greatly appreciated!
Rich
PS I’ve tried changing filename.cc to filename.cpp etc.
It looks to me like the linker can’t resolve the function call to add(), which means that you’re probably not compiling in add.cc properly. If I remember correctly, you should be doing something like this:
c++ main.cc add.cc -o out.exe
Aaah. Nice one. Yes that worked a charm. Thank you Alex.
So the compiling syntax is:
C++ mainfile.cc Inclue1.cc Include2.cc … IncludeN.cc -o out.exe
where InlcudeN are the N additional header files to be read in mainfile.
Is that a generic compiling syntax, or is this just specific to Cygwin???
Thanks again!
It’s generic to gcc/unix style compilers as far as I know.
for some reason my compiler ( i’m useing bloodshed versoin 4.somthing )keeps saying that cout and cin are undeclared. i have wrote several programms before including fixeing Fluxx’s rectangle area calculator and they all have compiled and ran smoothly up until now. i have included both iostream and my own header file ( ADD.h ).here is my code:
#include <iostream> #include "ADD.h" int main() { cout << "enter a number: "; int x; cin >> x; cout << "you entered "<< x <<" enter a number to add to this: " int y; cin >> y; cout << "the sum of these two numers is "<< add(x, y) << endl; system ("puase") return 0; }my header file for the add function is identical to yours ( only i named the file ADD.h instead of add.h ) .i have tryed rearanging them, retyping them, even writeing a whole new program. i’ve been stuck on this for days and i can’t see what i’m doing wrong. please help me Alex.
You forgot to put a ; (semi-colon) after
” enter a number to add to this: “
Also the statement spell error:
system (“puase”)
should be “pause” and need a semi-colon at the end.
sorry about that last comment i figured out what i was doing wrong just as i finished posting it, i forgot to include the “using namespace std” thing. but now i have another problem: everything else comiles fine but i keep getting a linker error. it says that i have an undefined referance to add. i don’t know what i’m doing wrong.i’m using the same code only i fixed the “name space” issue and filled in all the missing ;’s at the end of some of the lines.
Did you actually define the add() function? If you defined it in another .cpp file (eg. add.cpp), are you sure you are compiling that .cpp file into your program? You probably need to add it to your project or compile command line.
so I need my main program, a header file, and a sepreate .cpp file to define add? and how would I include the .cpp file for the add function? would I just place it affter my ADD.h header file in the
“# include” list? ex.
so I made a .cpp file defineing add and included it in my program ( the .cpp file defining add is the same as the one in this lesson ). but when I tryed to compile the program, it gave me an error. it was complaining about a linker error to win16 or somthing like that. to be honest, i havent got the slihtest clue what it means by win16 ( exept that I think it might have something to do the windows operating system files???).
If you’re using a MS compiler, on the left hand side you should see your project and a list of all the files include in it. If you right click on “Source Files” and choose “add” you can add new files or existing files to your project. That’s where you need to add the file.
Using #include with .cpp is almost never something you’ll have need of.
Header files sound really cool, because I could make a header file that had a function in it that would calculate the angle of the sun depending on the time/day of year etc, and put it on the internet for people to download :P (along with some instructions as to what functions to call in the main.cpp)
I’m not advanced enough yet to calculate the angle of the sun but that would still be cool :D
I understand this whole tutorial.. except I couldn’t work out how to create a “.h” file :S
I’m using Code::Blocks and when I create a new file it makes me save it as a “.cpp”
Edit:
Woooaahh nevermind, I just figured it out. :D
Awesome tutorials btw :)
Generally it’s a better idea to define your functions in .cpp files. If you wanted, you could distribute both the .cpp (containing the code) and a .h (containing a prototype for people to #include).
Amazing tutorials! It actually all makes sense LOL — now do one on the economy for the new U.S. administration LOL Thank you very, very much for making these tutorials!!! Alex, is there a cd I can buy of these tutorials from you? Or a book you wrote? I would donate, but who knows, next week the website could be down :(
Sorry, there is currently no offline version of the site. It’s something I’d like to do but I just don’t have the time to put it together right now.
This website has been running since May 2007, so we’ve been up for over a year and a half. As long as the meager advertising revenue exceeds the cost of hosting the site, it’ll probably be here. :)
Hi Alex,
This tutorial is awesome and I cant believe I’m finally learning C++.
I have a question. I was trying to compile the code you gave, it sounds crazy but should I add a header file in the header files folder or source files folder. Anyways I tried creating in both but none worked. I created the header file with .h extension.
#include <iostream> #include "add.h" int main() { using namespace std; cout << "enter the values of xand y: " << endl; int x,y; cin >> x; cin >> y; cout << add(x,y) << endl; return 0; }and the header file was
#ifndef ADD_H #define ADD_H int add(int x, int y); // function prototype for add.h { return x+y; } #endifI had an error:
1>—— Build started: Project: HelloWorld, Configuration: Debug Win32 ——
1>Linking…
1>MSVCRTD.lib(crtexe.obj) : error LNK2019: unresolved external symbol _main referenced in function ___tmainCRTStartup
1>C:\Documents and Settings\sravan\My Documents\Visual Studio 2008\Projects\HelloWorld\Debug\HelloWorld.exe : fatal error LNK1120: 1 unresolved externals
1>Build log was saved at “file://c:\Documents and Settings\sravan\My Documents\Visual Studio 2008\Projects\HelloWorld\HelloWorld\Debug\BuildLog.htm”
1>HelloWorld – 2 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Please help I am badly stuck here.
Thanks in advance.
Never mind Alex I got it.
This tutorial is really really helpful.
I wish we have a tutorial for java too, please tell me if you have one…
Thanks again.
Glad you got it working. Sorry, no Java tutorial from me since I don’t know the language.
excellent tutorials(thank you!) but I have 3 questions.
I don’t get the header file part.
In the example you use add.cpp as the declaration for add(). In add.h you put in a forward declaration for add(). But why can’t you define add() in the header file, isn’t that more efficient since you don’t need add.cpp anymore and thus less files = less work.
Second question (assuming you answered my first question):
You use add.cpp as a declaration file for add(), is it common to use a .cpp file with more then one declarations? Meaning multiple function declarations in one .cpp file (seems more convenient) or do you have to use multiple cpp files for multiple function declarations?
My last question:
Will these tutorials lead to the explaination of actually using your knowledge of c++ in developing programs? I think that’s really important because: okay I learned c++, now how do I use my knowledge? Like this tutorial gives you an assignment to make a program in the end.
Many thanks, keep it up!
You _could_ define add() in the header file if you wanted, but this is generally not done (unless the function is trivial, like 1 or 2 statements). Header files are generally used for prototyping functions and declaring classes, and then those things are actually implemented in .cpp files.
It is VERY common to have multiple functions in one .cpp file. Typically a .cpp file will contain a whole set of related function (eg. math.cpp will contain functions to do square roots, exponents, and other mathy things).
To address your last question, no, not really. It’s really up to you to figure out how to apply what you learn. At some point I’d love to go back and add that, but I haven’t had time. :(
WOW!!!!!!! Finally I get it. I had to have a add.cpp file and a main.cpp file and a add.h file! I’m sure I’ll be reading all these tutorials over again because I can never understand everything the first time around even at a snails pace. Just knowing that I finally figured it out though is the best part and seeing my mistake from the last section makes it all the better. Thanks for the tutorials :-) I’ve gotten this far after my first day. But I’m sure I’ll be reading these tutorials over and over to fully understand everything! Thanks again.
It is always a good idea to go over good, rich materials twice. I believe that the things you learn later on (not specifically in this tutorial, but anything) will help you better understand the basics when you go over them again. Generally, as you build a programmer mindset and learn to think, reason and think accordingly, I believe you will also find it easier to put things into perspective, so you might finally understand basic things you never understood the first thing you saw them.
hi it is my first project i need to add header files after #include “stdafx.” i am working on vs2005 my code
#include "stdafx.h" #include "cstdio" #include "cstdlib" #include "image.h" #include "misc.h" #include "pnmfile.h" #include "segment-image.h" using namespace segc; int main(int argc, char **argv) { the rest of code }all of header files are stored in the same folder with the rest of project
THE PROBLEM:
while bulding this message
Error 2 fatal error C1083: Cannot open include file: ‘image.h’: No such file or directory c:\documents and settings\xppresp3\my documents\visual studio 2005\projects\segc++\segc++\segment-image.h 23
i hope answer very fast.
thanks
THE PROBLEM AT SEGMENT_IMAGE.H BE SURE HEADER FILES ARE WRITTEN
#INCLUDE “HEADER FILE NAME . H “
Please post your code also, it will be easier for others to see what might be wrong and help you out.
agreee with above, looks like you have in your code
#include “image.h”
but in the path to your image its called segment-image.h
therefore should be
#include “segment-image.h”
How do i create a header in Dev C++? your help would be appreciated
In order to create a header file in dev-cpp, in the upper-left corrner there is a ‘new’ button (button with a pic of a blank peice of paper on it), click on this. once the file is created, right click the filename in the left hand column, and select rename. Enter the new name for the file and put .h at the end of the name. This will state it as being a header file and thus cuase the linker to treat it as such.
-Tyler
what does “int” stand for or represent?
int = integer, it is a basic numeric type with no decimals.
Alex, this is an awesome website, thanks for making it available.
My question is if the function file needs the stdafx.h header in microsoft visual basic 2008?
[ I have no idea, I've never used visual basic before. -Alex ]
Great tutorial and thanks for taking the time to respond to people’s questions. I have one myself. I am using Code Blocks 8.02 with Ubuntu 9.04.
main.cpp
#include <iostream> #include "add.h" int main() { using namespace std; cout << "The sum of 3 and 4 is: " << add(3, 4) << endl; return 0; }here is my add.cpp
int add(int x, int y) { return x + y; }here is my add.h
Now every time I try to build this program I get this error.
any help with what I am doing wrong would be great. Thanks
I don’t see anything wrong with the code. Sounds like an OS-specific issue. Perhaps ask on a Ubuntu forum?
For gcc compiler you may require to declare the function as extern “C” or the linker won’t link it properly. Try the following header file
#ifndef ADD_H #define ADD_H #ifdef __cplusplus extern "C" { #endif int add(int x, int y); // function prototype for add.h #ifdef __cplusplus } #endif #endifHey Alex, these tutorials are awesome! :] I’m learning a whole lot.
Thank you for making them.
This is probably something really obvious, but I am really confused.
I’m using Microsoft Visual C++ 2008 Edition, and when I add the add.cpp file, it automatically gives me an add.h file as well. But when I open it, in the tab it says add.h [Design] and there’s just a box named add, and I can’t put code anywhere.
I realized that there is a seperate folder specifically for Header files, but I couldn’t create an add.h file in it, because the name is already used. So I created one with a different name (with a .h extension), and it gave me a .cpp and a .h for that, too. And the .h is still a design box.
I’m probably going to feel really dumb after this, but where am I suppose to put the header code? D:
I have like 8 files and I only need to use three…so confusing >:
Also, the .cpp files had #include “theirname.h” on the top,
should I leave that there?
SALAM
THIS IS VERY IMPORTANT AND AMAIZING
IT IS IN VERY SIMPLE FORM THAT ANYONE CAN UNDERSTAND
I REALLY APPRICIATE AND THATNKS TO THE AUTHOUR
I was sent a .hpp file with nothing else and was wondering how to execute or read it or anything. Thank you for any help.
Try right clicking on the file and then select edit. If that doesn’t work you can change the file extension to .txt and then open it.
http://www.cplusplus.com/forum/beginner/5882/
this link deals with this question in forums.
Did you mean to write or in that short “History lesson”?
(The part that sticks out, just to make it easier to find for you)
Thanks for Codes !
sdklfjp
Why actually make header files? why not just define the functions you need after main?
Hey Alex, thanks for the awesome tutorial, i had major problems and confusions on how to actually write the header files, but now i understand it more. :)
Hi guys,
The article confuses me when it talks about the history what happened when C was standardized. I think the confusion starts when you introduce the runtime library, the built-in header and custom header, and the two .cpp files. Further, there is this step called linking and then the executable.
Now I am a programmer in JavaScript so I know some things. However, I was under the assumption that I could have a library of predefined and predeclared functions and just start using them or borrowing them in my core cpp files. But this wrap up seems to disturb my judgement and I am like what? Can someone explain the theoretical meaning and purpose of each file/header/component? How are they related to libraries/dll(s)? And so on.
Alright, I am a slow learner so I am rereading chap 1-5 again. hard thing for me to grasp is the breaking it down into functions. This program below is only way I could figure out how to get it to work. also i cannot figure out how to switch it from char to string and pass the info to another function:
MAIN.CPP
#include <iostream> #include <stdlib.h> #include "generate.h" int main() { using namespace std; int ns; cout << " Enter the Number of Students in your class? "; cin >> ns; generate(ns); return (0); }GENERATE.CPP
#include <iostream> #include <stdlib.h> #include "result.h" int generate(int ns) { using namespace std; int hs = 1, s_Score[25], s_Age[25]; char s_Name[25]; for (int count=1; count <= ns; count++) { system("clear"); cout << "Enter Student number, " << count << " of " << ns << " Information!" << endl << endl; cout << " Students name? "; cin >> s_Name[count]; cout << "n Students Score? "; cin >> s_Score[count]; cout << "nStudents age? "; cin >> s_Age[count]; if (count == 1) hs = count; if (s_Score[count] > s_Score[hs]) hs = count; } int a,b; char c; a = s_Age[hs]; b = s_Score[hs]; c = s_Name[hs]; result(hs, a, b, c); return (ns); }RESULT.CPP
#include <iostream> #include <stdlib.h> int result(int hs, int a, int b, char c) { using namespace std; system("clear"); cout << "This student had the Highest Score" << endl; cout << "Student: " << c << endl; cout << "Score: " << b << endl; cout << "Age: " << a << endl; return (hs); }GENERATE.H
RESULT.H
This Program works outside the compiler warning about whitespaces in GENERATE.H. outside of that it runs and functions. This program was alot easier to write it all in main() then to break it up into functions lol. but I am really trying to grasp functions cause it is the correct way from the tutorial to do it in the long run.
So if you can critique me, I could learn by example.
Best Regards
ps: below is program all in main()
// Ask for The number of students, enter there name, score and age and give the highest grad student output information. #include <fstream> #include <iostream> #include <stdlib.h> using namespace std; int main() { int ns, hs = 1, s_Score[25], s_Age[25]; string s_Name[25]; cout << " Enter the Number of Students in your class? "; cin >> ns; for (int count=1; count <= ns; count++) { system("clear"); cout << "Enter Student number, " << count << " of " << ns << " Information!" << endl << endl; cout << " Students name? "; cin >> s_Name[count]; cout << "n Students Score? "; cin >> s_Score[count]; cout << "nStudents age? "; cin >> s_Age[count]; if (count == 1) hs = count; if (s_Score[count] > s_Score[hs]) hs = count; } system("clear"); cout << "This student had the Highest Score" << endl; cout << "Student: " << s_Name[hs] << endl; cout << "Score: " << s_Score[hs] << endl; cout << "Age: " << s_Age[hs] << endl; return (0); }Sorry about the above. I just noticed I should of posted this to forums. its a little past topic of where this tutorial is at presently.
i am not to understand the header files then,please listout the header file names.
using namespace std;
i have made a main.cpp program that call a sum function .
i also define a header file add.h.also include this in main.cpp.
but error is coming.
please send me egg. of these type program i shall highly tham=nk full to you.
[...] The #ifndef, #define, and #endif statements are what is called a “header guard” which is used by the C compiler to check if our ParticleEmitter class has already been included in the program. If it has not, the compiler registers the header file for us which in turn allows us to create instances of the ParticleEmitter class. If you attempt to include a header file more than once, the compiler will complain and your program will probably crash. Header guards help prevent against this. You can read more about them here. [...]
Dear Alex,
Thanks a million for this comprehensive and thorough C++ course!
Unfortunately, I got stuck on this chapter, because it wasn’t clear to me I had to include the add.cpp file along with the header; I thought the header replaced the add.cpp file.
I got it now, though.
“This way, older programs that include
do not need to be rewritten”
You write this towards the bottom of the page… not that it matters but I’m a stickler for little errors… you meant to write “iostream.h” and you wrote “iosteam.h” (you missed the “r”)… just thought I should let you know :)
so far a WONDERFUL C++ course… very easy to understand, wonderful examples, and I’m able to fly though it :) thank you
When I compile, I get this error:
[Linker error] undefined reference to `__cpu_features_init’
What do I do?
Hi Alex – I’m having some issues with this –
my code is identical to the website – and I have no add.cpp in this project
when my code is this
#include <iostream> #include "add.h" // this brings in the declaration for add() int add(int x, int y); int main() { using namespace std; cout << "The sum of 3 and 4 is " << add(3, 4) << endl; return 0; }I get the error “add(int, int)” not defined
but when I change to this
#include <iostream> #include "add.h" // this brings in the declaration for add() int add(int x, int y); int main() { using namespace std; cout << "The sum of 3 and 4 is " << ADD_H(3, 4) << endl; return 0; }it works
I am guessing that this is because the header file only is added when ADD_H is included somewhere in main due to the if statements – but what happens when there is more than one function prototype in the library?
I figured it out! So you need main.cpp, add.cpp and add.h all in the same folder because the main is including add.h which calls add.cpp to define what “int add()” is! Now my question is, how can you use files in different folders?
Hi
I have these files :
- node.h:
#ifndef _NODE_H_ #define _NODE_H_ class node { public: int temp; void output(); }; #endif- node.cpp:
#include "node.h" #include <iostream> using namespace std; void node::output() { cout<<"Ehsan"<<endl; }- main.cpp (containing int mian())
Now, which one shoud be included in mian.cpp? (I use g++ in order to compile main.cpp)
Someone answer me please (as soon as possible)
When I include node.cpp in main.cpp, main.cpp can be compiled, but when I include node.h in main.cpp, I get errors!
What should I do if I want to include node.h in main.cpp?
Where is the node.h file saved to? The compiler always looks for header files in the same directory as where the main.cpp is located.
If this is not the problem, please post your full code and list of errors so that we can further assist you.
-Tyler