MSVC 多行宏编译器错误

Question

I have a macro defined in a header, the function that the macro is based on is also in the same header.

Here is a very basic example, not the exact code but hopefully it gives enough to illustrate the problem:

myMacro.h:

    #ifndef MYMACRO_H
        #define MYMACRO_H

        #ifdef _DEBUG
            bool myAssertFn(int test, char const* desc, char const* file, int line) {
                if (test != 0) {
                //Test passes, no action required
                    return true;
                }
                std::string msg;

                if (desc != nullptr) {
                    msg += "\n Context: ";
                    msg += desc;
                }
                if (file != NULL) {
                    msg += "\n    File: ";
                    msg += file;
                }
                if (line > 0) {
                    msg += "\n    Line: ";
                    msg += std::to_string(line);
                }
                //Construct filename
                time_t tClock = time(0);
                char szTime[24];
                tm tmNow;
                //Get system time
                localtime_s(&tmNow, &tClock);
                //Assertion Log File, path and name
                static const char* assertLogFile = "./ALF.log";
                //Build time / date of day prefix
                sprintf_s(szTime, sizeof(szTime), "%04d/%02d/%02d %02d:%02d:%02d "
                        , tmNow.tm_year + 1900, tmNow.tm_mon + 1, tmNow.tm_mday
                        , tmNow.tm_hour, tmNow.tm_min, tmNow.tm_sec);
                //Does file exist?
                std::ofstream logFile(assertLogFile, std::ios_base::app);
                //Write the content to the file
                logFile << szTime << msg.c_str() << std::endl;
                return false;
            }
            //Macro
            #define myAssert(test, desc)\               
                        myAssertFn((test), (desc), __FILE__, __LINE__)      
        #else
            #define myAssert(test, desc)\
                        (void)0
        #endif
    #endif

The purpose of this macro is to include debug information and be a replacement for the standard assert function with the added benefit of logging the results to a file.

The issue is when compiling I get:

error C2065: 'test' : undeclared identifier
error C2065: 'desc' : undeclared identifier

Other errors where the macro is used in a source file:

error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
error C2365: 'myAssertFn' : redefinition; previous definition was 'function' myAssert.h(37) : see declaration of 'myAssertFn'
error C2078: too many initializers
error C2143: syntax error : missing ';' before 'const'

In any source file that needs this macro I simply include the header and use the macro as follows:

    myAssert(ptr != NULL, "ptr != NULL");

If the test returns 0 then the description will be logged to file with a date, time stamp, the file name and the line number the fault occurs at.

Answer 1

When you do your define, you have trailing characters :

#define myAssert(test, desc)\               
                              ^^^^^^^^^^^^^^

That means that your backslash applies on a space and not on the endline, so myAssertFn((test), (desc), __FILE__, __LINE__) usage not part of the macro anymore.

Your errors on the source file likely comes from the fact that you didn't remove the definition from the header file, so there is a redefinition error.

Answer 2

With multi-line macros the \\ character must be the very last on the line.

Even whitespaces will disrupt multi-line macros and you have multiple spaces at the end of the line.