std::string operator+=

since C++20

// (1) Non const version only
constexpr basic_string& operator+=( const basic_string& str );

// (2) Non const version only
constexpr basic_string& operator+=( CharT ch );

// (3) Non const version only
constexpr basic_string& operator+=( const CharT* s );

// (4) Non const version only
constexpr basic_string& operator+=( std::initializer_list<CharT> ilist );

// (5) Non const version only
template < class StringViewLike >
constexpr basic_string& operator+=( const StringViewLike& t );

since C++17

// (1) Non const version only
basic_string& operator+=( const basic_string& str );

// (2) Non const version only
basic_string& operator+=( CharT ch );

// (3) Non const version only
basic_string& operator+=( const CharT* s );

// (4) Non const version only
basic_string& operator+=( std::initializer_list<CharT> ilist );

// (5) Non const version only
template < class StringViewLike >
basic_string& operator+=( const StringViewLike& t );

since C++11

// (1) Non const version only
basic_string& operator+=( const basic_string& str );

// (2) Non const version only
basic_string& operator+=( CharT ch );

// (3) Non const version only
basic_string& operator+=( const CharT* s );

// (4) Non const version only
basic_string& operator+=( std::initializer_list<CharT> ilist );

until C++11

// (1) Non const version only
basic_string& operator+=( const basic_string& str );

// (2) Non const version only
basic_string& operator+=( CharT ch );

// (3) Non const version only
basic_string& operator+=( const CharT* s );

Appends additional characters to the string.

• (1) Appends string str.
• (2) Appends character ch.
• (3) Appends the null-terminated character string pointed to by s.
• (4) Appends characters in the initializer list ilist.
• (5) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then appends characters in the string view sv as if by append(sv).
  Overload Resolution

  This overload participates in overload resolution only if std::is_convertible_v<const StringViewLike&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const StringViewLike&, const CharT*> is false.

Parameters

• str - string to append
• ch - character value to append
• s - pointer to a null-terminated character string to append
• ilist - std::initializer_list with the characters to append
• t - object (convertible to std::basic_string_view) with the characters to append

Return value

*this

Complexity

important

This section requires improvement. You can help by editing this doc page.

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

Exceptions

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

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

Notes

caution

Overload (2) can accept any types that are implicitly convertible to CharT.
For std::string, where CharT is char, the set of acceptable types includes all arithmetic types.

This may have unintended effects.

Example

Main.cpp

#include <iostream>
#include <iomanip>
#include <string>
 
int main()
{
   std::string str;
   str.reserve(50); //reserves sufficient storage space to avoid memory reallocation
   std::cout << std::quoted(str) << '\n'; //empty string
 
   str += "This";
   std::cout << std::quoted(str) << '\n';
 
   str += std::string(" is ");
   std::cout << std::quoted(str) << '\n';
 
   str += 'a';
   std::cout << std::quoted(str) << '\n';
 
   str += {' ','s','t','r','i','n','g','.'};
   std::cout << std::quoted(str) << '\n';
 
   str += 76.85; // equivalent to str += static_cast<char>(76.85), might not be the intent
   std::cout << std::quoted(str) << '\n';
}

Output

""
"This"
"This is "
"This is a"
"This is a string."
"This is a string.L"