# std::basic_string<CharT,Traits,Allocator>::replace

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< cpp‎ | string‎ | basic string

basic_string& replace( size_type pos, size_type count, const basic_string& str ); | (1) |
basic_string& replace( const_iterator first, const_iterator last, const basic_string& str ); | (1) |
| (2) |
basic_string& replace( size_type pos, size_type count, const basic_string& str, size_type pos2, size_type count2 ); |  | (until C++14)
basic_string& replace( size_type pos, size_type count, const basic_string& str, size_type pos2, size_type count2 = npos ); |  | (since C++14)
template< class InputIt > basic_string& replace( const_iterator first, const_iterator last, InputIt first2, InputIt last2 ); | (3) |
basic_string& replace( size_type pos, size_type count, const CharT* cstr, size_type count2 ); | (4) |
basic_string& replace( const_iterator first, const_iterator last, const CharT* cstr, size_type count2 ); | (4) |
basic_string& replace( size_type pos, size_type count, const CharT* cstr ); | (5) |
basic_string& replace( const_iterator first, const_iterator last, const CharT* cstr ); | (5) |
basic_string& replace( size_type pos, size_type count, size_type count2, CharT ch ); | (6) |
basic_string& replace( const_iterator first, const_iterator last, size_type count2, CharT ch ); | (6) |
basic_string& replace( const_iterator first, const_iterator last, std::initializer_list <CharT> ilist ); | (7) | (since C++11)
template < class T > basic_string& replace( size_type pos, size_type count, const T& t ); | (8) | (since C++17)
template < class T > basic_string& replace( const_iterator first, const_iterator last, const T& t ); | (8) | (since C++17)
template < class T > basic_string& replace( size_type pos, size_type count, const T& t, size_type pos2, size_type count2 = npos ); | (9) | (since C++17)

Replaces the part of the string indicated by either `[pos, pos + count)` or `[first, last)` with a new string.

The new string can be one of:

1) string `str`;
2) substring `[pos2, pos2 + count2)` of `str`, except if count2==npos or if would extend past str.size(), `[pos2, str.size())` is used.
3) characters in the range `[first2, last2)`.

This overload has the same effect as overload (6) if `InputIt` is an integral type. | (until C++11)
This overload only participates in overload resolution if `InputIt` qualifies as an LegacyInputIterator. | (since C++11)

4) characters in the range `[cstr, cstr + count2)`;
5) characters in the range `[cstr, cstr + Traits::length(cstr))`;
6) `count2` copies of character `ch`;
7) characters in the initializer list `ilist`;
8) characters of a string view `sv`, converted from `t` as if by std::basic_string_view <CharT, Traits> sv = t;. These overloads only participate in overload resolution if std::is_convertible_v <const T&, std::basic_string_view <CharT, Traits>> is true and std::is_convertible_v <const T&, const CharT*> is false
9) subview `[pos2, pos2 + count2)` of a string view `sv`, converted from `t` as if by std::basic_string_view <CharT, Traits> sv = t;, except if count2==npos or if it would extend past sv.size(), `[pos2, sv.size())` is used. This overload only participates in overload resolution if std::is_convertible_v <const T&, std::basic_string_view <CharT, Traits>> is true and std::is_convertible_v <const T&, const CharT*> is false.

### Parameters

pos | - | start of the substring that is going to be replaced
count | - | length of the substring that is going to be replaced
first, last | - | range of characters that is going to be replaced
str | - | string to use for replacement
pos2 | - | start of the substring to replace with
count2 | - | number of characters to replace with
cstr | - | pointer to the character string to use for replacement
ch | - | character value to use for replacement
first2, last2 | - | range of characters to use for replacement
ilist | - | initializer list with the characters to use for replacement
t | - | object (convertible to std::basic_string_view) with the characters to use for replacement

### Return value

*this

### Exceptions

std::out_of_range if `pos > length()` or `pos2 > str.length()`

std::length_error if the resulting string will exceed maximum possible string length (max_size())

In any case, if an exception is thrown for any reason, this function has no effect (strong exception guarantee). (since C++11)

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 2946 | C++17 | `string_view` overload causes ambiguity in some cases | avoided by making it a template

### Example

Run this code

    #include <iostream>
    #include <string>

    int main()
    {
        std::string str("The quick brown fox jumps over the lazy dog.");

        str.replace(10, 5, "red"); // (5)

        str.replace(str.begin(), str.begin() + 3, 1, 'A'); // (6)

        std::cout << str << '\n';
    }

Output:

    A quick red fox jumps over the lazy dog.

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