Standards / Extensions | C or C++ | Dependencies |
---|---|---|
Language Environment | both |
#include <stdio.h>
#include <stdio_ext.h>
size_t __fpending(FILE *stream);
#define _OPEN_SYS_UNLOCKED 1
#include <stdio.h>
#include <stdio_ext.h>
size_t __fpending_unlocked(FILE *stream);
The __fpending() function retrieves the number of bytes pending to be written in the output buffer associated with the specified binary stream. When the stream is opened for text processing, the __fpending() function retrieves the number of characters pending to be written.
The __fpending_unlocked() function is equivalent to the __fpending() function with the exception that it is not thread-safe. This function can be safely used in a multithreaded application if it is called while the invoking thread owns the (FILE *) object, such as after a successful call to either the flockfile() or ftrylockfile() function.
The __fpending() function cannot be used on buffers in read mode or opened read-only.
The __fpending() functions return the number of bytes or characters pending to be written in the current buffer, depending on the type of stream. Otherwise, the __fpending() functions return 0. If an error has occurred, __fpending() functions return 0 and set errno to nonzero.
When the stream is wide-oriented text, the __fpending() functions return a value measured in wide characters.
An application wishing to check for error situations should set errno to 0, then call __fpending(), and then check errno. If errno is nonzero, assume that an error has occurred.
/* CELEBF89
This example writes and reads data to a file while querying the
stream for information about data in the I/O buffer.
*/
#include <stdio.h>
#include <stdio_ext.h>
void main() {
FILE *f;
char filename[FILENAME_MAX] = "myfile.dat";
char data[128] = "There are 34 bytes in this buffer\n";
int datalen = strlen(data);
size_t n = 0;
f = fopen(filename,"wb+");
if (f == NULL) {
perror("fopen() failed\n");
return;
}
if (__fwritable(f)) printf("Writing is allowed on the open stream\n");
if (__freadable(f)) printf("Reading is allowed on the open stream\n");
n = fputs(data,f);
if (n == EOF) {
perror("fputs() failed\n");
return;
}
n = __fpending(f);
printf("There are %d bytes in the buffer pending to be written\n", n);
if (__fwriting(f)) printf("The last operation on the stream was a write\n");
rewind(f);
n = fgetc(f);
n = __freadahead(f);
printf("There are %d bytes remaining to be read from the buffer\n", n);
if (__freading(f)) printf("The last operation on the stream was a read\n");
return;
}
Writing is allowed on the open stream
Reading is allowed on the open stream
There are 34 bytes in the buffer pending to be written
The last operation on the stream was a write
There are 33 bytes remaining to be read from the buffer
The last operation on the stream was a read