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

From cppreference.net
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 ( ) ) ; .

Contents

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)