__flbf() — Determine if a stream is line buffered

Standards

Standards / Extensions	C or C++	Dependencies
Language Environment	both	None

Format

#include <stdio.h>
#include <stdio_ext.h>

int __flbf(FILE *stream);

General description

The __flbf() function determines if the specified stream is line buffered.

Returned value

The __flbf() function returns nonzero if the stream is line buffered. Otherwise, the __flbf() function returns 0. If an error has occurred, __flbf() returns 0 and sets errno to nonzero.

An application wishing to check for error situations should set errno to 0, then call __flbf(), and then check errno. If errno is nonzero, assume that an error has occurred.

Error Code: Description
EBADF: The stream specified by stream is not valid.

Example

CELEBF84

/* CELEBF84

   This example flushes all the line-buffered files.
   
*/ 

#include <stdio.h>
#include <stdio_ext.h>
#include <string.h>

#define BUF_SIZE 128

int main(void)
{
   char lbuf[BUF_SIZE]; /* line buffer */
   char fbuf[BUF_SIZE]; /* full buffer */
   char *tagstr = "This file was modified!";
   FILE *lfp;
   FILE *ffp;

   lfp = fopen("newlfile.dat", "a+");
   if(lfp == NULL){
      perror("Open file failed!\n");
      return -1;
   }
   if(setvbuf(lfp, lbuf, _IOLBF, sizeof(lbuf)) != 0){ /* set lbuf to line-buffered */
      perror("Format line-buffered failed!\n");
      fclose(lfp);
      return -1;
   }

   if (__flbf(lfp)) printf("newlfile.dat is line-buffered\n");
   else printf("newlfile.dat is not line-buffered\n");

   if(fwrite(lfp,strlen(tagstr), 1, lfp) != 1){ /* write tag string to line buffer*/
      perror("Write line buffer failed!\n");
      fclose(lfp);
      return -1;
   }
   printf("Write to the line buffered file succeeded\n");

   ffp = fopen("newffile.dat", "a+");
   if(ffp == NULL){
      perror("Open file failed!\n");
      fclose(lfp);
      return -1;
   }
   if(setvbuf(ffp, fbuf, _IOFBF, sizeof(fbuf)) != 0){ /* set fbuf to full-buffered */
      perror("Format full-buffered failed!\n");
      fclose(ffp);
      return -1;
   }

   if (__flbf(ffp)) printf("newffile.dat is line-buffered\n");
   else printf("newffile.dat is not line-buffered\n");

   if(fwrite(tagstr, strlen(tagstr), 1, ffp) != 1){ /* write tag string to full buffer */
      perror("Write full buffer failed!\n");
      fclose(lfp);
      fclose(ffp);
      return -1;
   }
   printf("Write to the full buffered file succeeded\n");
   _flushlbf(); /* flush line buffered files */
   printf("Only line buffered files are flushed...\n");
   fclose(lfp);
   fclose(ffp);
   return 0;
}

Output

newlfile.dat is line-buffered
Write to the line buffered file succeeded
newffile.dat is not line-buffered
Write to the full buffered file succeeded
Only line buffered files are flushed...