抠下VS2008里assert的实现

自己一直不怎么用assert，主要是因为以前感觉貌似assert不是标准里提供的，而是特定编译器提供的

刚才查了查C语言他爸那本书，

原来在附录里提到了assert

B.6部分

（直接拷贝文字，中文字符乱码，所以拷贝了图片）

查了查VS2008中具体实现

如下：

#define assert(_Expression) (void)( (!!(_Expression)) || (_wassert(_CRT_WIDE(#_Expression), _CRT_WIDE(__FILE__), __LINE__), 0) )

注意，这个地方_wasser这个w是因为VS2008中工程默认字符集为Unicode，即宽字符集

!!(_Expression)

两个感叹号的做法在某些地方常见到，比较巧妙

作用为把各种值转为0或者1

比如!!5 == 1

!!0 == 0

具体实现为

#ifdef _UNICODE
void __cdecl _wassert (
        const wchar_t *expr,
        const wchar_t *filename,
        unsigned lineno
        )
#else  /* _UNICODE */
void __cdecl _assert (

        const char *expr,
        const char *filename,
        unsigned lineno
        )
#endif  /* _UNICODE */
{
        /*
         * Build the assertion message, then write it out. The exact form
         * depends on whether it is to be written out via stderr or the
         * MessageBox API.
         */
        if ( (_set_error_mode(_REPORT_ERRMODE)== _OUT_TO_STDERR) ||
             ((_set_error_mode(_REPORT_ERRMODE) == _OUT_TO_DEFAULT) &&
              (__app_type == _CONSOLE_APP)) )
        {
#ifdef _UNICODE
            {
                TCHAR assertbuf[ASSERTBUFSZ];
                HANDLE hErr ;
                DWORD written;

                hErr = GetStdHandle(STD_ERROR_HANDLE);

                if(hErr!=INVALID_HANDLE_VALUE && hErr!=NULL)
                {
                    if(swprintf(assertbuf, ASSERTBUFSZ,_assertstring,expr,filename,lineno) >= 0)
                    {
                        if(GetFileType(hErr) == FILE_TYPE_CHAR)
                        {
                            if(WriteConsoleW(hErr, assertbuf, (unsigned long)wcslen(assertbuf), &written, NULL))
                            {
                                abort();
                            }
                        }
                    }
                }
            }

#endif  /* _UNICODE */

            /*
             * Build message and write it out to stderr. It will be of the
             * form:
             *        Assertion failed: <expr>, file <filename>, line <lineno>
             */
            if ( !anybuf(stderr) )
            /*
             * stderr is unused, hence unbuffered, as yet. set it to
             * single character buffering (to avoid a malloc() of a
             * stream buffer).
             */
             (void) setvbuf(stderr, NULL, _IONBF, 0);


            _ftprintf(stderr, _assertstring, expr, filename, lineno);
            fflush(stderr);

        }
        else {
            int nCode;
            TCHAR * pch;
            TCHAR assertbuf[ASSERTBUFSZ];
            TCHAR progname[MAX_PATH + 1];

            /*
             * Line 1: box intro line
             */
            _ERRCHECK(_tcscpy_s( assertbuf, ASSERTBUFSZ, BOXINTRO ));
            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dblnewline ));

            /*
             * Line 2: program line
             */
            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, PROGINTRO ));

            progname[MAX_PATH] = _T('\0');
            if ( !GetModuleFileName( NULL, progname, MAX_PATH ))
                _ERRCHECK(_tcscpy_s( progname, MAX_PATH + 1, _T("<program name unknown>")));

            pch = (TCHAR *)progname;

            /* sizeof(PROGINTRO) includes the NULL terminator */
            if ( (sizeof(PROGINTRO)/sizeof(TCHAR)) + _tcslen(progname) + NEWLINESZ > MAXLINELEN )
            {
                pch += ((sizeof(PROGINTRO)/sizeof(TCHAR)) + _tcslen(progname) + NEWLINESZ) - MAXLINELEN;
                _ERRCHECK(_tcsncpy_s( pch, (MAX_PATH + 1) - (pch - progname), dotdotdot, DOTDOTDOTSZ ));
            }

            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, pch ));
            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, newline ));

            /*
             * Line 3: file line
             */
            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, FILEINTRO ));

            /* sizeof(FILEINTRO) includes the NULL terminator */
            if ( (sizeof(FILEINTRO)/sizeof(TCHAR)) + _tcslen(filename) + NEWLINESZ > MAXLINELEN )
            {
                size_t p, len, ffn;

                pch = (TCHAR *) filename;
                ffn = MAXLINELEN - (sizeof(FILEINTRO)/sizeof(TCHAR)) - NEWLINESZ;

                for ( len = _tcslen(filename), p = 1;
                      pch[len - p] != _T('\\') && pch[len - p] != _T('/') && p < len;
                      p++ );

                /* keeping pathname almost 2/3rd of full filename and rest
                 * is filename
                 */
                if ( (ffn - ffn/3) < (len - p) && ffn/3 > p )
                {
                    /* too long. using first part of path and the
                       filename string */
                    _ERRCHECK(_tcsncat_s( assertbuf, ASSERTBUFSZ, pch, ffn - DOTDOTDOTSZ - p ));
                    _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dotdotdot ));
                    _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, pch + len - p ));
                }
                else if ( ffn - ffn/3 > len - p )
                {
                    /* pathname is smaller. keeping full pathname and putting
                     * dotdotdot in the middle of filename
                     */
                    p = p/2;
                    _ERRCHECK(_tcsncat_s( assertbuf, ASSERTBUFSZ, pch, ffn - DOTDOTDOTSZ - p ));
                    _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dotdotdot ));
                    _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, pch + len - p ));
                }
                else
                {
                    /* both are long. using first part of path. using first and
                     * last part of filename.
                     */
                    _ERRCHECK(_tcsncat_s( assertbuf, ASSERTBUFSZ, pch, ffn - ffn/3 - DOTDOTDOTSZ ));
                    _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dotdotdot ));
                    _ERRCHECK(_tcsncat_s( assertbuf, ASSERTBUFSZ, pch + len - p, ffn/6 - 1 ));
                    _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dotdotdot ));
                    _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, pch + len - (ffn/3 - ffn/6 - 2) ));
                }

            }
            else
                /* plenty of room on the line, just append the filename */
                _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, filename ));

            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, newline ));

            /*
             * Line 4: line line
             */
            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, LINEINTRO ));
            _ERRCHECK(_itot_s( lineno, assertbuf + _tcslen(assertbuf), ASSERTBUFSZ - _tcslen(assertbuf), 10 ));
            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dblnewline ));

            /*
             * Line 5: message line
             */
            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, EXPRINTRO ));

            /* sizeof(HELPINTRO) includes the NULL terminator */

            if (    _tcslen(assertbuf) +
                    _tcslen(expr) +
                    2*DBLNEWLINESZ +
                    (sizeof(INFOINTRO)/sizeof(TCHAR)) - 1 +
                    (sizeof(HELPINTRO)/sizeof(TCHAR)) > ASSERTBUFSZ )
            {
                _ERRCHECK(_tcsncat_s( assertbuf, ASSERTBUFSZ, expr,
                    ASSERTBUFSZ -
                    (_tcslen(assertbuf) +
                    DOTDOTDOTSZ +
                    2*DBLNEWLINESZ +
                    (sizeof(INFOINTRO)/sizeof(TCHAR))-1 +
                    (sizeof(HELPINTRO)/sizeof(TCHAR)))));
                _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dotdotdot ));
            }
            else
                _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, expr ));

            _ERRCHECK(_tcscat_s( assertbuf, ASSERTBUFSZ, dblnewline ));

            /*
             * Line 6, 7: info line
             */

            _ERRCHECK(_tcscat_s(assertbuf, ASSERTBUFSZ, INFOINTRO));
            _ERRCHECK(_tcscat_s(assertbuf, ASSERTBUFSZ, dblnewline ));

            /*
             * Line 8: help line
             */
            _ERRCHECK(_tcscat_s(assertbuf, ASSERTBUFSZ, HELPINTRO));

            /*
             * Write out via MessageBox
             */

            nCode = __crtMessageBox(assertbuf,
                _T("Microsoft Visual C++ Runtime Library"),
                MB_ABORTRETRYIGNORE|MB_ICONHAND|MB_SETFOREGROUND|MB_TASKMODAL);

            /* Abort: abort the program */
            if (nCode == IDABORT)
            {
                /* raise abort signal */
                raise(SIGABRT);

                /* We usually won't get here, but it's possible that
                   SIGABRT was ignored.  So exit the program anyway. */

                _exit(3);
            }

            /* Retry: call the debugger */
            if (nCode == IDRETRY)
            {
                _DbgBreak();
                /* return to user code */
                return;
            }

            /* Ignore: continue execution */
            if (nCode == IDIGNORE)
                return;
        }

        abort();
}