function

std::operator+ (string)

string (1)	string operator+ (const string& lhs, const string& rhs);
c-string (2)	string operator+ (const string& lhs, const char* rhs);string operator+ (const char* lhs, const string& rhs);
character (3)	string operator+ (const string& lhs, char rhs);string operator+ (char lhs, const string& rhs);

string (1)

string operator+ (const string& lhs, const string& rhs);

c-string (2)

string operator+ (const string& lhs, const char*   rhs);string operator+ (const char*   lhs, const string& rhs);

character (3)

string operator+ (const string& lhs, char          rhs);string operator+ (char          lhs, const string& rhs);

string (1)	string operator+ (const string& lhs, const string& rhs);string operator+ (string&& lhs, string&& rhs);string operator+ (string&& lhs, const string& rhs);string operator+ (const string& lhs, string&& rhs);
c-string (2)	string operator+ (const string& lhs, const char* rhs);string operator+ (string&& lhs, const char* rhs);string operator+ (const char* lhs, const string& rhs);string operator+ (const char* lhs, string&& rhs);
character (3)	string operator+ (const string& lhs, char rhs);string operator+ (string&& lhs, char rhs);string operator+ (char lhs, const string& rhs);string operator+ (char lhs, string&& rhs);

string (1)

string operator+ (const string& lhs, const string& rhs);string operator+ (string&&      lhs, string&&      rhs);string operator+ (string&&      lhs, const string& rhs);string operator+ (const string& lhs, string&&      rhs);

c-string (2)

string operator+ (const string& lhs, const char*   rhs);string operator+ (string&&      lhs, const char*   rhs);string operator+ (const char*   lhs, const string& rhs);string operator+ (const char*   lhs, string&&      rhs);

character (3)

string operator+ (const string& lhs, char          rhs);string operator+ (string&&      lhs, char          rhs);string operator+ (char          lhs, const string& rhs);string operator+ (char          lhs, string&&      rhs);

Concatenate strings

Returns a newly constructed string object with its value being the concatenation of the characters in lhs followed by those of rhs.

In the signatures taking at least one rvalue reference as argument, the returned object is move-constructed by passing this argument, which is left in an unspecified but valid state. If both arguments are rvalue references, only one of them is moved (it is unspecified which), with the other one preserving its value.

Parameters

lhs, rhs: Arguments to the left- and right-hand side of the operator, respectively.
If of type char*, it shall point to a null-terminated character sequence.

Example

// concatenating strings
#include <iostream>
#include <string>

main ()
{
  std::string firstlevel ("com");
  std::string secondlevel ("cplusplus");
  std::string scheme ("http://");
  std::string hostname;
  std::string url;

  hostname = "www." + secondlevel + '.' + firstlevel;
  url = scheme + hostname;

  std::cout << url << '\n';

  return 0;
}

Output:

Return Value

A string whose value is the concatenation of lhs and rhs.

Complexity

Unspecified, but generally linear in the resulting string length (and linear in the length of the non-moved argument for signatures with rvalue references).

Iterator validity

The signatures with rvalue references may invalidate iterators, pointers and references related to the moved string.

Data races

The signatures with rvalue references modify the moved string.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in either string objects.

s is not a null-terminated character sequence, it causes undefined behavior.

If the resulting string length would exceed the max_size, a length_error exception is thrown.
A bad_alloc exception is thrown if the function needs to allocate storage and fails.