fwide ()- 确定流方向

格式

#include <stdio.h>
#include <wchar.h>
int fwide(FILE *stream, int mode);

语言级别

ANSI

线程安全

是

语言环境敏感

当在编译命令上指定 LOCALETYPE (*CLD) 时，此功能不可用。

集成文件系统界面

当在编译命令上指定 SYSIFCOPT (*NOIFSIO) 时，此功能不可用。

描述

fwide() 函数确定 stream指向的流的方向。如果方式大于 0 ，那么 fwide() 函数会首先尝试使流面向范围。如果方式小于 0 ，那么 fwide() 函数将首先尝试使流面向字节。否则， mode 为 0 ，并且 fwide() 函数不会改变流的方向。

注: 如果已确定流的方向，那么 fwide() 函数不会对其进行更改。

返回值

如果在调用后流具有宽方向，那么 fwide() 函数将返回大于 0 的值。如果流具有字节方向，那么它将返回小于 0 的值。如果流没有方向，那么它将返回 0。

示例

#include <stdio.h>
#include <math.h>
#include <wchar.h>
 
void check_orientation(FILE *stream)
{
   int rc;
   rc = fwide(stream,0);      /* check the orientation */
   if (rc<0) {
      printf("Stream has byte orientation.\n");
   } else if (rc>0)  {
      printf("Stream has wide orientation.\n");
   } else {
      printf("Stream has no orientation.\n");
   }
   return;
}
 
int main(void)
{
   FILE *stream;
   /* Demonstrate that fwide can be used to set the orientation,
      but cannot change it once it has been set.   */
   stream = fopen("test.dat","w");
   printf("After opening the file: ");
   check_orientation(stream);
   fwide(stream, -1);        /* Make the stream byte oriented */
   printf("After fwide(stream, -1): ");
   check_orientation(stream);
   fwide(stream,  1);        /* Try to make the stream wide oriented */
   printf("After fwide(stream,  1): ");
   check_orientation(stream);
   fclose(stream);
   printf("Close the stream\n");
   /* Check that a wide character output operation sets the orientation
      as expected.   */
   stream = fopen("test.dat","w");
   printf("After opening the file: ");
   check_orientation(stream);
   fwprintf(stream, L"pi = %.5f\n", 4* atan(1.0));
   printf("After fwprintf( ): ");
   check_orientation(stream);
   fclose(stream);
   return 0;
   /*******************************************************************
      The output should be similar to :
      After opening the file: Stream has no orientation.
      After fwide(stream, -1): Stream has byte orientation.
      After fwide(stream,  1): Stream has byte orientation.
      Close the stream
      After opening the file: Stream has no orientation.
      After fwprintf( ): Stream has wide orientation.
   *******************************************************************/
}