Question

error LNK2019: unresolved external symbol “char * __cdecl
BytesToString(unsigned char const *,unsigned int)”
(?BytesToString@@YAPADPBEI@Z) referenced in function
_wmain C:\Users\anandada\Documents\Visual Studio 2010\Projects\ByteToString\ByteToString\ByteToString.obj ByteToString

above is the error I am getting. code is shown below. ByteToString is a console Win32 application and Utility is Win32 DLL.

Utility.c

#include "stdafx.h"
#include "Utility.h"
#include "stdlib.h"

char* BytesToString( const unsigned char* PpcbBytes, const unsigned int PuiNoOfBytes)
{
    unsigned char bRetVal = 0;
    unsigned int ctr = 0;
    char* PpszString = NULL;
    int len=0;

    do
    {
        PpszString=(char*)calloc(PuiNoOfBytes*3+1,sizeof(char));
        if(NULL==PpszString)
            break;
        len=5;
    } while(0);
    return PpszString;
}

Utility.h

#ifndef _UTILITY_H
#define _UTILITY_H
__declspec(dllexport) char* BytesToString( const unsigned char* PpcbBytes, const unsigned int PuiNoOfBytes);
#endif

ByteToString.cpp

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

#include "stdafx.h"
#include "string.h"
#include "stdlib.h"
#include "..\Utility\Utility.h"

int _tmain(int argc, _TCHAR* argv[])
{
    unsigned char pbArray[5]={0x41,0x42,0x43,0x44,0x45};
    char* pbExpArray=NULL;
    unsigned int Flag=1;
    int len=0;

    pbExpArray=BytesToString(pbArray,5);
    free(pbExpArray);
    Flag=strcmp("41 42 43 44 45 ",pbExpArray);
    len=strlen(pbExpArray);

    return 0;
}

I have set project properties like this:

both ByteToString and Utility project calling conventions are: __cdecl

In ByteToString, Linker->General->Additional Directories: $(OutDir)

(I tried this too Linker->General->Additional Directories:$(SolutionDir)$(Configuration)\ )

In ByteToString, Linker->Input->Additional Dependenicies: Utility.lib

I aslo tried this,

#ifndef _UTILITY_H
#define _UTILITY_H
extern "C"
{
__declspec(dllexport) char* BytesToString( const unsigned char* PpcbBytes, const unsigned int PuiNoOfBytes);
}
#endif

This gives error:

error C2059: syntax error : ‘string’

Update:

1. While creating project, I had added Utility.cpp. I renamed it to Utility.c, set the project properties and compiled. I got the error shown above.
2. Then I renamed it back to Utility.cpp and compiled. No error.

Why is this? I want Utility file in .c. What is the correct method to add a .c file into project?

Answer 1

You need the header file to differentiate between use in the exporting DLL and the consuming other module (DLL or EXE). The project wizard had generated a preprocessor definition for this purpose. If your exporting DLL is called Utility.dll than this definitions is UTILITY_EXPORTS. Check you projects properties for this.

In your header file you define something like this

#ifdef UTILITY_EXPORTS
#define UTILITY_API __declspec(dllexport)
#else
#define UTILITY_API __declspec(dllimport)
#endif

#ifdef __cplusplus
extern "C" {
#endif 

UTILITY_API char* BytesToString( const unsigned char* PpcbBytes, const unsigned int PuiNoOfBytes);

#ifdef __cplusplus
}
#endif

This causes the consuming project to use the symbol in the import library, that you have added to the consuming module.