[C/C++标准库]_[初级]_[使用freopen重定向标准输出]

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freopen

场景:

1.比如控制台打打印太长了，需要记录到文件上分析。

2.或者是做一些简单的日志工作就可以用到freopen。

代码:

#include <stdlib.h>#include <stdio.h>#include <string.h>#include <string>#include <iostream>#include <io.h>#include <assert.h>using namespace std;char *GetFileDirectory(const char *filename) {      char *ret = NULL;      char dir[1024];      char *cur;      if (filename == NULL) return(NULL);    #if defined(WIN32) && !defined(__CYGWIN__)  #   define IS_SEP(ch) ((ch=='/')||(ch=='\\'))  #else  #   define IS_SEP(ch) (ch=='/')  #endif      strncpy(dir, filename, 1023);      dir[1023] = 0;      cur = &dir[strlen(dir)];      while (cur > dir)       {          if (IS_SEP(*cur)) break;                    cur --;      }      if (IS_SEP(*cur))       {          if (cur == dir)          {              //1.根目录              dir[1] = 0;          }          else           {              *cur = 0;          }          ret = strdup(dir);      }       else       {          //1.如果是相对路径,获取当前目录          //io.h          if (getcwd(dir, 1024) != NULL)           {              dir[1023] = 0;              ret = strdup(dir);          }      }      return ret;  #undef IS_SEP  } int main(int argc,char*argv[]){printf("file is %s\n",argv[0]);char* dir = GetFileDirectory(argv[0]);printf("dir is %s\n",dir);string dirs(dir);free(dir);dirs.append("/").append("log.txt");FILE* file = freopen(dirs.c_str(),"w",stdout); assert(file == stdout); printf("I am write into log.txt,not print to screen\n"); cout << "hello" << endl; fclose(stdout);string openFile("notepad.exe "); openFile.append(dirs.c_str()); system(openFile.c_str()); //注意:如果你想重置restore stdout,那么最好一开始就不要使用freopen重定向. //http://c-faq.com/stdio/undofreopen.html //如果非要重置就参考以下文章吧: //http://stackoverflow.com/questions/1908687/how-to-redirect-the-output-back-to-the-screen-after-freopenout-txt-a-stdo return 0;}

打开文件.log.txt:

I am write into log.txt,not print to screenhello

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