Initializing std :: string with the return value of the function, is there a copy?

Question

I have the following code, I use GCC and C ++ 11:

std::string system_call(const char *cmd){
   std::string a;
   ...
   return a;
}

std::string st = system_call("whatever code");

Is there an implicit copy there? I call this function many times, and I assume that it executes a copy from the return value system_callto the variable st, and then frees the temporary value of r.

Is there any way to avoid copying? Using st.swap(system_call())throws and errors in the compiler:

error: there is no corresponding function to call 'Stand :: basic_string :: swap (std :: string)

My questions:

• If there is a problem or not
• How to avoid this, if any

thank

EDIT: . , , , st - .

system_call("whatever").swap(st);

Answer 1

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Answer 2

Elision - , , , .

std::string system_call(const char *cmd){
  std::string a;
  ...
  return a; // all return paths return `a` directly
}

std::string st = system_call("whatever code");

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Answer 3

c++11, , c++11.

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