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std::basic_string::append

basic_string& append( size_type count, CharT ch );	(1)
basic_string& append( const basic_string& str );	(2)
	(3)
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)
basic_string& append( const CharT* s, size_type count );	(4)
basic_string& append( const CharT* s );	(5)
template< class InputIt > basic_string& append( InputIt first, InputIt last );	(6)
basic_string& append( std::initializer_list<CharT> ilist );	(7)	(since C++11)
template < class T > basic_string& append( const T& t );	(8)	(since C++17)
template < class T > basic_string& append( const T& t, size_type pos, size_type count = npos );	(9)	(since C++17)

Appends additional characters to the string.

1) Appends count copies of character ch

2) Appends string str

3) Appends a substring [pos, pos+count) of str. If the requested substring lasts past the end of the string, or if count == npos, the appended substring is [pos, size()). If pos > str.size(), std::out_of_range is thrown.

4) Appends the first count characters of character string pointed to by s. s can contain null characters.

5) Appends the null-terminated character string pointed to by s. The length of the string is determined by the first null character.

6) Appends characters in the range [first, last). This overload has the same effect as overload (1) if InputIt is an integral type.

7) Appends characters from the initializer list ilist.

8) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then appends all characters from sv as if by append(sv.data(), sv.size()). 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.

9) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then appends the characters from the subview [pos, pos+count) of sv. If the requested subview extends past the end of sv, or if count == npos, the appended subview is [pos, sv.size()). If pos >= sv.size(), std::out_of_range is thrown. 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

count	-	number of characters to append
pos	-	the index of the first character to append
ch	-	character value to append
first, last	-	range of characters to append
str	-	string to append
s	-	pointer to the character string to append
ilist	-	initializer list with the characters to append
t	-	object convertible to `std::basic_string_view` 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 an exception is thrown for any reason, this function has no effect (strong exception guarantee). (since C++11).

If the operation would result in size() > max_size(), throws std::length_error.

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

#include <string>
#include <iostream>
 
int main() {
    std::basic_string<char> str = "string";
    const char* cptr = "C-string";
    const char carr[] = "Two and one";
 
    std::string output;
 
    // 1) Append a char 3 times. 
    // Notice, this is the only overload accepting chars.
    output.append(3, '*');
    std::cout << "1) " << output << "\n";
 
    //  2) Append a whole string
    output.append(str);
    std::cout << "2) " << output << "\n";
 
    // 3) Append part of a string (last 3 letters, in this case)
    output.append(str, 3, 3);
    std::cout << "3) " << output << "\n";
 
    // 4) Append part of a C-string
    // Notice, because `append` returns *this, we can chain calls together
    output.append(1, ' ').append(carr, 4);
    std::cout << "4) " << output << "\n";
 
    // 5) Append a whole C-string
    output.append(cptr);
    std::cout << "5) " << output << "\n";
 
    // 6) Append range
    output.append(&carr[3], std::end(carr));
    std::cout << "6) " << output << "\n";
 
    // 7) Append initializer list
    output.append({ ' ', 'l', 'i', 's', 't' });
    std::cout << "7) " << output << "\n";
}

Output:

1) ***
2) ***string
3) ***stringing
4) ***stringing Two 
5) ***stringing Two C-string
6) ***stringing Two C-string and one
7) ***stringing Two C-string and one list

operator+=	appends characters to the end (public member function)
strcat	concatenates two strings (function)
strncat	concatenates a certain amount of characters of two strings (function)
wcscat	appends a copy of one wide string to another (function)
wcsncat	appends a certain amount of wide characters from one wide string to another (function)