error LNK2019: unresolved external symbol referenced in function main

Question

Am trying to run my simple assembly code in C++.I have only two files ".cpp" file and ".asm" file. On compiling it gives an error (see below ).I would appreciate if anyone could help...:)

This is my "main.cpp" file

#include <iostream>
using namespace std;

extern "C" int GetValueFromASM(); 

int main(int argc, char *argv[]){

cout<<"value is:"<<GetValueFromASM()<<endl;
cin.get();

return 0;
}

Also i have a simple "asm.asm" file

.code
   GetValueFromASM proc
   mov rax,3254
   ret
   GetValueFromASM endp
end

When try to build i get this error :

1>main.obj : error LNK2019: unresolved external symbol GetValueFromASM referenced in             
function main

1>..\visual studio 2012\Projects\AllAssembly\x64\Debug\AllAssembly.exe : fatal error LNK1120: 1 unresolved externals

I tried go to PROPERTIES->LINKS->ADDITIONAL LIBRARY DIRECTORIES and change the path but it didn't work.

I tried also go to LINKER->SYSTEM->SUBSYSTEM and Select "Windows (/SUBSYSTEM:WINDOWS)" or "Console (/SUBSYSTEM:CONSOLE)" but neither one worked. Can anyone help !!..BIG THANKS

Answer 1

extern "C" implies a leading underscore (c-style function naming). Just prefix your function in .asm file and it'll start linking.

UPD: if your project does not build, be sure, you included MASM build customizations: go to project Context Menu -> Build Customizations... -> check the tickbox for masm (.targets, .props).

Then go to properties of you .asm file and select Item Type as 'Microsoft Macro Assembler'.