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Function fseek () in C

The function int fseek (FILE * stream, long int offset, int whence) in Standard C library sets the Stream file location to the given offset . The offset parameter specifies the number of bytes to search from where the given location is.

Declare function fseek () in C

Below is the declaration for fseek () function in C:

 int fseek ( FILE * stream , long int offset , int whence )

Parameters

stream - This is the pointer to a FILE object that identifies the Stream.

offset - This is the number of bytes to offset the word.

whence - This is the position from which the offset is added. It is determined by one of the following constants:

Hang DescriptionSEEK_SET File header SEEK_CUR Current position of SEEK_END file pointer File end

Returns the value

This function returns 0 if successful. If not, the function returns a value other than 0.

For example

The following program C illustrates the usage of the fseek () function in C:

 #include int main () { FILE * fp ; fp = fopen ( "baitapc.txt" , "w+" ); fputs ( "Hoc C co ban va nang cao tai QTM !!!" , fp ); fseek ( fp , 4 , SEEK_SET ); fputs ( " lap trinh C" , fp ); fclose ( fp ); return ( 0 ); }

Compiling and running the above program will create a baitapc.txt with the following content. At the beginning, the program created the file and recorded the lesson with high quality in QTM !!! but then we have restored the cursor written at the 4th position starting at the beginning of the file and using the command puts ().

Now monitor the following contents of the above file by using the following C program:

 #include int main () { FILE * fp ; int c ; fp = fopen ( "baitapc.txt" , "r" ); while ( 1 ) { c = fgetc ( fp ); if ( feof ( fp ) ) { break ; } printf ( "%c" , c ); } fclose ( fp ); return ( 0 ); }

Compile and run the above C program to see the results:

According to Tutorialspoint

Previous lesson: Function freopen () in C

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