You may receive an "error C2593: 'operator <<' is ambiguous" error message when you try to pass an __int64 variable to the ostream operator <<

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Article ID: 168440
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If you try to pass an __int64 variable to the ostream operator <<, you get the following error:
error C2593: 'operator <<' is ambiguous


There is no operator << for __int64 type defined for the ostream class.


Define your own version of operator <<. The following sample code section shows a simple solution for << operator that converts the __int64 variable to a char * type and passes it to the ostream << operator.


Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section.

This problem was corrected in Microsoft Visual C++ .NET.

More information

The following sample program demonstrates the problem and workaround:
// Compiler Options : /GX

//#define WORKAROUND   //Uncomment this line to workaround

using namespace std;

std::ostream& operator<<(std::ostream& os, __int64 i )
    char buf[20];
    sprintf(buf,"%I64d", i );
    os << buf;
    return os;


int main(){
__int64  i64;

cout << i64 ;

return 0;


Article ID: 168440 - Last Review: June 22, 2014 - Revision: 5.0
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