CODEWITHSUNDEEP
c++
Boying
Boying

Reputation: 1434

C++ function overloading confusing for string reference and anonymous function

I defined following functions for string processing:

void sub(const std::string & repl){
}

void sub(std::function<std::string()> userfun){
}

When I call with an anonymous function, it is OK

sub([=](){return "a"; });

But when I call with string, it has failed

sub("a");

error C2668: 'sub' : ambiguous call to overloaded function

Is it possible to avoid ambiguous call when calling with a string against anonymous function parameter

Using Visual C++ 2013

UPDATE2

Create a new console project and put everyting from sketch and still failed in VC++2013

// overload.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <string>
#include <functional>
void sub(const std::string & repl) {
}

void sub(std::function<std::string()> userfun) {

}
int _tmain(int argc, _TCHAR* argv[])
{
    sub("a");
    return 0;
}

1>------ Build started: Project: overload, Configuration: Debug Win32 ------
1>Build started 2016-06-22 17:55:00.
1>InitializeBuildStatus:
1>  Touching "Debug\overload.tlog\unsuccessfulbuild".
1>ClCompile:
1>  overload.cpp
1>c:\users\xxxxxx\documents\visual studio 2013\projects\overload\overload\overload.cpp(15): error C2668: 'sub' : ambiguous call to overloaded function
1>          c:\users\xxxxxx\documents\visual studio 2013\projects\overload\overload\overload.cpp(10): could be 'void sub(std::function<std::string (void)>)'
1>          c:\users\xxxxxx\documents\visual studio 2013\projects\overload\overload\overload.cpp(7): or       'void sub(const std::string &)'
1>          while trying to match the argument list '(const char [2])'
1>
1>Build FAILED.
1>

UPDATE: My VS about information: enter image description here

Upvotes: 1

Views: 246

Answers (1)

Bathsheba
Bathsheba

Reputation: 234825

It's a compiler bug: sub(std::string("a")); is an adequate workaround. (Binding an anonymous temporary to a const reference is legal in C++.)

MSVC2013 compiles the statement

std::function<std::string()> foo("a");

Showing that "a" is a valid constructor argument for that type. (It appears to be using, in error, the constructor function( std::nullptr_t )).

Reference: http://en.cppreference.com/w/cpp/utility/functional/function/function

Upvotes: 3

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