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17.7 — std::string inserting

By Alex, on July 18th, 2010

Inserting

Inserting characters into an existing string can be done via the insert() function.

string& string::insert (size_type index, const string& str)
string& string::insert (size_type index, const char* str)

  • Both functions insert the characters of str into the string at index
  • Both function return *this so they can be “chained”.
  • Both functions throw out_of_range if index is invalid
  • Both functions throw a length_error exception if the result exceeds the maximum number of characters.
  • In the C-style string version, str must not be NULL.

Sample code:

string sString("aaaa");
cout << sString << endl;

sString.insert(2, string("bbbb"));
cout << sString << endl;

sString.insert(4, "cccc");
cout << sString << endl;

Output:

aaaa
aabbbbaa
aabbccccbbaa

Here’s a crazy version of insert() that allows you to insert a substring into a string at an arbitrary index:

string& string::insert (size_type index, const string& str, size_type startindex, size_type num)

  • This function inserts num characters str, starting from startindex, into the string at index.
  • Returns *this so it can be “chained”.
  • Throws an out_of_range if index or startindex is out of bounds
  • Throws a length_error exception if the result exceeds the maximum number of characters.

Sample code:

string sString("aaaa");

const string sInsert("01234567");
sString.insert(2, sInsert, 3, 4); // insert substring of sInsert from index [3,7) into sString at index 2
cout << sString << endl;

Output:

aa3456aa

There is a flavor of insert() that inserts the first portion of a C-style string:

string& string::insert(size_type index, const char* str, size_type len)

  • Inserts len characters of str into the string at index
  • Returns *this so it can be “chained”.
  • Throws an out_of_range exception if the index is invalid
  • Throws a length_error exception if the result exceeds the maximum number of characters.
  • Ignores special characters (such as ‘\0′)

Sample code:

string sString("aaaa");

sString.insert(2, "bcdef", 3);
cout << sString << endl;

Output:

aabcdaa

There’s also a flavor of insert() that inserts the same character multiple times:

string& string::insert(size_type index, size_type num, char c)

  • Inserts num instances of char c into the string at index
  • Returns *this so it can be “chained”.
  • Throws an out_of_range exception if the index is invalid
  • Throws a length_error exception if the result exceeds the maximum number of characters.

Sample code:

string sString("aaaa");

sString.insert(2, 4, 'c');
cout << sString << endl;

Output:

aaccccaa

And finally, the insert() function also has three different versions that use iterators:

void insert(iterator it, size_type num, char c)
iterator string::insert(iterator it, char c)
void string::insert(iterator it, InputIterator begin, InputIterator end)

  • The first function inserts num instances of the character c before the iterator it.
  • The second inserts a single character c before the iterator it, and returns an iterator to the position of the character inserted.
  • The third inserts all characters between [begin,end) before the iterator it.
  • All functions throw a length_error exception if the result exceeds the maximum number of characters.

A.1 — Static and dynamic libraries
Index
17.6 — std::string appending
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