函數(shù)fseek使用指南
1.函數(shù)原型：
int fseek ( FILE * stream, long int offset, int origin );
2. 函數(shù)功能：
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.
3. 函數(shù)參數(shù)
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).
4. 返回值
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.
5. 例程
#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:
This is a sample
