18、通过可变参数实现打印日志

在c和c++中，可变参数使用的最多函数有：scanf，printf，以及fprintf，fscanf，sprintf等，MFC也提供CString::Format实现可变参数。

本示例通过va_list来实现自己的可变参数函数，实现程序写日志功能。

通过可变参数实现日志打印

// ForATest.cpp : 定义控制台应用程序的入口点。
#include " stdafx.h "
#include " Windows.h "
#include " iostream "
using namespace std;
#include " string "
#include < stdio.h >
#include < stdarg.h >
#define PL_ERROR -2
#define SERVICE_ERROR(strMod, ulErrCode, cFormat, ...) \
logRecord(__FUNCTION__, __LINE__, strMod, PL_ERROR, ulErrCode, cFormat, __VA_ARGS__);
static string TestIT_MODULE = " TestItMe " ;
void logRecord( string strFunc,
int iLine,
string strMod,
int iLevel,
int iErrCode,
char * cFormat,
...)
{
string strLog;
strLog.clear();
char acBuffer1[ 255 ], acBuffer2[ 255 ];
sprintf_s(acBuffer1, 254 , " [%s] [%d] [%s] [%d] [%d] " , strFunc.data(), iLine, strMod.data(), iLevel, iErrCode);
va_list args;
va_start (args, cFormat);
vsprintf(acBuffer2,cFormat, args);
FILE * pFile = fopen( " C:\\log.txt " , " a+ " );
if (NULL == pFile)
return ;
fprintf(pFile, acBuffer1);
fprintf(pFile, acBuffer2);
fprintf(pFile, " \n " );
fclose(pFile);
va_end(args);
}
int _tmain( int argc, _TCHAR * argv[])
{
string strFileName = " C:\\Intel\\Logs " ;
SERVICE_ERROR(TestIT_MODULE, - 1 , " GetFile %s Attributes fail error code %d " , strFileName.data(), GetLastError());
}

sprintf_s的一个示例

#include < stdio.h >
#include " string "
#include " iostream "
using namespace std;
int main( void )
{
char buffer[ 200 ], s[] = " computer " , c = ' l ' ;
int i = 35 , j;
float fp = 1.7320534f ;
string name = " hello " ;
// Format and print various data:
j = sprintf_s( buffer, 200 , " String: %s\n " , s );
j += sprintf_s( buffer + j, 200 - j, " Character: %c\n " , c );
j += sprintf_s( buffer + j, 200 - j, " Integer: %d\n " , i );
j += sprintf_s( buffer + j, 200 - j, " Real: %f\n " , fp );
j += sprintf_s( buffer + j, 200 - j, " Name: %s\n " , name.data() );
printf_s( " Output:\n%s\ncharacter count = %d\n " , buffer, j );
}

C++ version 

// AssistTest.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include "cstdio"
#include "iostream"
#include "string"
#include "fstream"
#include "cstdarg"
#include "windows.h"

using namespace std;

const int OP_SUCCESS = 0;
const int OP_FAILED = -1;
static string TestIT_MODULE = "TestItMe";

#define SERVICE_ERROR(strMod, ulErrCode, cFormat, ...) \
    logRecord(__FUNCTION__, __LINE__, strMod, ulErrCode, cFormat, __VA_ARGS__);

//print log module
void logRecord(string strFunc,
               int iLine,
               string strMod,
               int iErrCode,
               char* cFormat,
               ...)
{
    string strLog;
    strLog.clear();
    char acBuffer1[255], acBuffer2[255];
    sprintf_s(acBuffer1, 254, "[%s] [%d] [%s] [%d] ", strFunc.data(), iLine, strMod.data(), iErrCode);
    va_list args;
    va_start (args, cFormat);
    vsprintf(acBuffer2,cFormat, args);

    ofstream ofLogFile;
    ofLogFile.open("F:\\log.txt", ios::out | ios::app);
    if (!ofLogFile)
    {
        return;
    }

    string strBuffer1, strBuffer2;
    strBuffer1 = acBuffer1;
    strBuffer2 = acBuffer2;

    ofLogFile.write(strBuffer1.data(), strBuffer1.size());
    ofLogFile.write(strBuffer2.data(), strBuffer2.size());
    ofLogFile.put('\n');
    ofLogFile.close();

    va_end(args);
}

int main(int argc, char* argv[])
{
    string strFileName = "C:\\Intel\\Logs";
    SERVICE_ERROR(TestIT_MODULE, -1, "GetFile %s Attributes fail error code %d", strFileName.data(), GetLastError());
}

C++ version 2

// AssistTest.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include "cstdio"
#include "iostream"
#include "string"
#include "fstream"
#include "cstdarg"
#include "windows.h"

using namespace std;

const int OP_SUCCESS = 0;
const int OP_FAILED = -1;
static string TestIT_MODULE = "TestItMe";

class mt
{
public:
    void LogRecord(string strFunc, unsigned int uiLine, string strMod, int iulErrCode, char* cFormat, ...);
    //print log module
};

void mt::LogRecord(string strFunc,
                   unsigned int uiLine,
                   string strMod,
                   int iErrCode,
                   char* cFormat,
                   ...)
{
    string strLog;
    strLog.clear();
    char acBuffer1[255], acBuffer2[255];
    sprintf_s(acBuffer1, 254, "[%s] [%d] [%s] [%d] ", strFunc.data(), uiLine, strMod.data(), iErrCode);
    va_list args;
    va_start (args, cFormat);
    vsprintf(acBuffer2,cFormat, args);

    ofstream ofLogFile;
    ofLogFile.open("F:\\log.txt", ios::out | ios::app);
    if (!ofLogFile)
    {
        return;
    }

    string strBuffer1, strBuffer2;
    strBuffer1 = acBuffer1;
    strBuffer2 = acBuffer2;

    ofLogFile.write(strBuffer1.data(), strBuffer1.size());
    ofLogFile.write(strBuffer2.data(), strBuffer2.size());
    ofLogFile.put('\n');
    ofLogFile.close();

    va_end(args);
}

int main(int argc, char* argv[])
{
    string strFileName = "C:\\Intel\\Logs";
    mt m1;
    m1.LogRecord(__FUNCTION__, __LINE__ ,TestIT_MODULE, -1, "GetFile %s Attributes fail error code %d", strFileName.data(), GetLastError());
}

参考

[1] http://www.cplusplus.com/reference/clibrary/cstdio/vsprintf/

[2] http://www.cnblogs.com/stuarts/archive/2010/08/03/1791598.html

[3] http://www.cnblogs.com/mydomain/archive/2010/07/27/1785667.html

讲述了了va_start等可变参数的基本概念及定义