function
<cstdio>
fseek
int fseek ( FILE * stream, long int offset, int origin );
Reposition stream position indicator
Sets the position indicator associated with the stream to a new position.
For streams open in binary mode, the new position is defined by adding offset to a reference position specified by origin.
For streams open in text mode, offset shall either be zero or a value returned by a previous call to ftell, and origin shall necessarily be SEEK_SET.
If the function is called with other values for these arguments, support depends on the particular system and library implementation (non-portable).
The end-of-file internal indicator of the stream is cleared after a successful call to this function, and all effects from previous calls to ungetc on this stream are dropped.
On streams open for update (read+write), a call to fseek allows to switch between reading and writing.
Parameters
- stream
- Pointer to a FILE object that identifies the stream.
- offset
- Binary files: Number of bytes to offset from origin.
Text files: Either zero, or a value returned by ftell.
- origin
- Position used as reference for the offset. It is specified by one of the following constants defined in <cstdio> exclusively to be used as arguments for this function:
| Constant | Reference position |
|---|
| SEEK_SET | Beginning of file |
| SEEK_CUR | Current position of the file pointer |
| SEEK_END | End of file * |
* Library implementations are allowed to not meaningfully support SEEK_END (therefore, code using it has no real standard portability).
Return Value
If successful, the function returns zero.
Otherwise, it returns non-zero value.
If a read or write error occurs, the error indicator (ferror) is set.
Example
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|
/* fseek example */
#include <stdio.h>
int main ()
{
FILE * pFile;
pFile = fopen ( "example.txt" , "wb" );
fputs ( "This is an apple." , pFile );
fseek ( pFile , 9 , SEEK_SET );
fputs ( " sam" , pFile );
fclose ( pFile );
return 0;
}
| |
After this code is successfully executed, the file example.txt contains:
See also
- ftell
- Get current position in stream (function
)
- fsetpos
- Set position indicator of stream (function
)
- rewind
- Set position of stream to the beginning (function
)