C ftell() function
C library function - ftell()
The ftell() function is used to obtain the current value of the file-position indicator for the stream pointed to by stream.
Syntax:
long int ftell(FILE *stream)
ftell() Parameters:
Name | Description | Required /Optional |
---|---|---|
stream | The opened (via fopen) stream. | Required |
Return value from ftell()
- The ftell() function returns the current file position. On error, ftell() and ftello() return –1, cast to long and off_t respectively, and set errno to a nonzero value.
Example: ftell() function
#include <stdio.h>
#define NUM_CHAR 6
#define NUM_ALPHA 26
int main(void)
{
FILE * stream;
int i;
char ch;
char buffer[NUM_ALPHA];
long position;
if (( stream = fopen("test.txt", "r")) != NULL )
{
/* read into buffer */
for ( i = 0; ( i < NUM_ALPHA/2 ) && ((buffer[i] = fgetc(stream)) != EOF ); ++i )
if (i==NUM_CHAR-1) /* We want to be able to position the */
/* file pointer to the character in */
/* position NUM_CHAR */
position = ftell(stream);
buffer[i] = '\0';
}
printf("Current file position is %d\n", position);
printf("Buffer contains: %s\n", buffer);
}
Output:
Current file position is 6 Buffer contains: C programming
Errors: The value of error number can be set to:
Value | Meaning |
---|---|
ENODEV | Operation was attempted on a wrong device. |
ENOTOPEN | The file is not open. |
ENUMMBRS | The file is open for multi-member processing. |
ENUMRECS | Too many records. |
ERECIO | The file is open for record I/O. |
ESTDERR | stderr cannot be opened. |
ESTDIN | stdin cannot be opened. |
ESTDOUT | stdout cannot be opened. |
EIOERROR | A non-recoverable I/O error occurred. |
EIORECERR | A recoverable I/O error occurred. |
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