关于fdopen的段错误问题，求助

[bw_0927]

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char ch[20];
    FILE *fp = fdopen("./tmp", "r+);
    fscanf(fp, "%s" , ch);
    printf("%s\n", ch);
    return 0;
}

仔细看了下man，好像fdopen的第一个参数是需要一个文件描述符，因此改成了下面的版本
int main()
{ 
    char ch[20];
    int fd = open("./tmp", O_RDWR);
    FILE *fp = fdopen(fd, "r+);
    fscanf(fp, "%s" , ch);
    printf("%s\n", ch);
    return 0;
}


tmp的文件内容是：
this is a test
this is a test
this is a test

是哪里出错了？谢谢

[bw_0927]

没有错哦，你说的地方都是对的

[赵4老师]

TCHAR.H Routine  _UNICODE & _MBCS Not Defined _MBCS Defined _UNICODE Defined 
_tfdopen _fdopen _fdopen _wfdopen 

/* _FDOPEN.C: This program opens a file using low-
 * level I/O, then uses _fdopen to switch to stream
 * access. It counts the lines in the file.
 */

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>

void main( void )
{
   FILE *stream;
   int  fh, count = 0;
   char inbuf[128];

   /* Open a file handle. */
   if( (fh = _open( "_fdopen.c", _O_RDONLY )) == -1 )
      exit( 1 );

   /* Change handle access to stream access. */
   if( (stream = _fdopen( fh, "r" )) == NULL )
      exit( 1 );

   while( fgets( inbuf, 128, stream ) != NULL )
      count++;

   /* After _fdopen, close with fclose, not _close. */
   fclose( stream );
   printf( "Lines in file: %d\n", count );
}

[ilwmin]

[Quote=引用 6 楼 bw_0927 的回复:]
没有错哦，你说的地方都是对的
[/Quote]
int fd = open("./tmp", O_RDWR);
我这里没问题.看一下这句的返回值是多少?如果是-1就肯定是路径不对.

[肥多罗]

看看tmp这个文件本身的权限，要不chmod 777 tmp 试试

[SLSnake]

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <io.h>
#include <share.h>

int main( void )
{
   FILE *stream;
   int  fd, count = 0;
   char inbuf[128];

   // Open a file.
   if( _sopen_s( &fd, "crt_fdopen.txt", _O_RDONLY, _SH_DENYNO, 0 ) )
      exit( 1 );

   // Get stream from file descriptor.
   if( (stream = _fdopen( fd, "r" )) == NULL )
      exit( 1 );

   while( fgets( inbuf, 128, stream ) != NULL )
      count++;

   // After _fdopen, close with fclose, not _close.
   fclose( stream );
   printf( "Lines in file: %d\n", count );
}

MSDN 上的例子,希望有帮助

[SLSnake]

FILE *fp = fdopen(fd, "r+");
应该这样

[bw_0927]

是疏忽写错了，源文件中就是这样的“FILE *fp = fdopen(fd, "r+");”

[SLSnake]

int main()
{ 
    char ch[20];
    int fd = _open("tmp", O_RDWR);
    FILE *fp = _fdopen(fd, "r+");
    fscanf(fp, "%s" , ch);
    printf("%s\n", ch);
    return 0;
}

VC6中成功运行,不知道楼主的问题解决没有

[SLSnake]

建议楼主检查下
int fd = open("./tmp", O_RDWR);
这句成功运行没有
怀疑路径是不是给错了

[zhangweiit]

段错误的话，那明显是内存问题了

你把char[20]再放大一点看一下
换成char ch[100];试试看