std::basic_string<CharT,Traits,Allocator>:: operator+=

Appends additional characters to the string.

Parameters

Return value

* this

Complexity

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 .

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

Notes

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

#include <iomanip>
#include <iostream>
#include <string>
 
int main()
{
    std::string str;
 
    // reserve sufficient storage space to avoid memory reallocation
    str.reserve(50);
 
    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 += 69.96; // Equivalent to str += static_cast<char>(69.96);
                  // 'E' (ASCII code 69) is appended by overload (2),
                  // which might not be the intent.
 
    // To add a numeric value, consider std::to_string():
    str += std::to_string(1729);
 
    std::cout << std::quoted(str) << '\n';
}

""
"This"
"This is "
"This is a"
"This is a string."
"This is a string.E1729"

Defect reports

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

See also