std::basic_string<CharT,Traits,Allocator>::append

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< cpp‎ | string‎ | basic string
 
C++
 
Strings library
 
std::basic_string
 
basic_string& append( size_type count, CharT ch );
 (1) (constexpr since C++20)
basic_string& append( const CharT* s, size_type count );
 (2) (constexpr since C++20)
basic_string& append( const CharT* s );
 (3) (constexpr since C++20)
template< class SV >
basic_string& append( const SV& t );
 (4) (since C++17)
(constexpr since C++20)
template< class SV >

basic_string& append( const SV& t, size_type pos,

                      size_type count = npos );
 (5) (since C++17)
(constexpr since C++20)
basic_string& append( const basic_string& str );
 (6) (constexpr since C++20)
(7)
basic_string& append( const basic_string& str,
                      size_type pos, size_type count );
 (until C++14)
basic_string& append( const basic_string& str,
                      size_type pos, size_type count = npos );
 (since C++14)
(constexpr since C++20)
template< class InputIt >
basic_string& append( InputIt first, InputIt last );
 (8) (constexpr since C++20)
basic_string& append( std::initializer_list<CharT> ilist );
 (9) (since C++11)
(constexpr since C++20)

Appends additional characters to the string.

1) Appends count copies of character ch.
2) Appends characters in the range [s, s + count).
If [s, s + count) is not a valid range, the behavior is undefined.
3) Equivalent to return append(s, Traits::length(s));.
4,5) Appends characters in a string view sv constructed from t.
  • If only t is provided, all characters in sv are appended.
  • If pos is also provided:
    • If count is npos, all characters in sv starting from pos are appended.
    • Otherwise, the std::min(count, sv.size() - pos) characters in sv starting from pos are appended.
These overloads participate in overload resolution only if all following conditions are satisfied:
4) Equivalent to std::basic_string_view<CharT, Traits> sv = t;
return append(sv.data(), sv.size());.
5) Equivalent to std::basic_string_view<CharT, Traits> sv = t;
return append(sv.substr(pos, count));.
6,7) Appends characters in another string str.
  • If only str is provided, all characters in it are appended.
  • If pos is also provided:
    • If count is npos, all characters in str starting from pos are appended.
    • Otherwise, the std::min(count, str.size() - pos) characters in str starting from pos are appended.
6) Equivalent to return append(str.data(), str.size());.
7) Equivalent to return append(std::basic_string_view<CharT, Traits>
                  (str).substr(pos, count));.
 (since C++20)
8) Equivalent to return append(basic_string(first, last, get_allocator()));.

This overload has the same effect as overload (1) if InputIt is an integral type.

(until C++11)

This overload participates in overload resolution only if InputIt satisfies the requirements of LegacyInputIterator.

(since C++11)
9) Equivalent to return append(ilist.begin(), ilist.size());.

Parameters

count - number of characters to append
ch - character value to append
s - pointer to the character string to append
t - object convertible to std::basic_string_view with the characters to append
pos - the index of the first character to append
str - string to append
first, last - range of characters to append
ilist - initializer list with the characters to append

Return value

*this

Complexity

There are no standard complexity guarantees, typical implementations behave similar to std::vector::insert().

Exceptions

If the operation would cause size() to exceed max_size(), throws std::length_error.

5) If pos > sv.size() is true, throws std::out_of_range.
7) If pos > str.size() is true, throws std::out_of_range.

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

Example

Run this code
#include <cassert>
#include <string>
 
int main()
{
    std::string str = "std::string";
    const char* cptr = "C-string";
    const char carr[] = "range";
 
    std::string result;
 
    // 1) Append a char 3 times.
    // Note: This is the only overload accepting “CharT”s.
    result.append(3, '*');
    assert(result == "***");
 
    // 2) Append a fixed-length C-string
    result.append(cptr, 5);
    assert(result == "***C-str");
 
    // 3) Append a null-terminated C-string
    // Note: Because “append” returns *this, we can chain calls together.
    result.append(1, ' ').append(cptr);
    assert(result == "***C-str C-string");
 
    // 6) Append a whole string
    result.append(1, ' ').append(str);
    assert(result == "***C-str C-string std::string");
 
    // 7) Append part of a string
    result.append(str, 3, 2);
    assert(result == "***C-str C-string std::string::");
 
    // 8) Append range
    result.append(&carr[2], &carr[3]);
    assert(result == "***C-str C-string std::string::n");
 
    // 9) Append initializer list
    result.append({'p', 'o', 's'});
    assert(result == "***C-str C-string std::string::npos");
}

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 847 C++98 there was no exception safety guarantee added strong exception safety guarantee
LWG 2250 C++98 the behavior of overload (7) was
undefined if pos > str.size() is true 		always throws an exception in this case
LWG 2788 C++98 overload (8) used a default constructed
allocator to construct the temporary string 		obtains the allocator
from get_allocator()
LWG 2946 C++17 overload (4) causes ambiguity in some cases avoided by making it a template

See also

(C++23)
 appends a range of characters to the end
(public member function)
appends characters to the end
(public member function)
concatenates two strings
(function)
concatenates a certain amount of characters of two strings
(function)
appends a copy of one wide string to another
(function)
appends a certain amount of wide characters from one wide string to another
(function)
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