Linux-function-truncate;

#include <unistd.h>

#include <sys/types>

int truncate (const char *path, off_t length);

int ftruncate (int fd,off_t length);

The truncate and ftruncate function cause the regular file named by path or referenced by FD to is truncated to a size of Precisely

Length bytes.

The/*truncate and Ftruncate functions are named by the parameter path or by a regular file pointed to by the parameter fd to a byte of the specified size of the parameter length */

If the file previously was larger then this size, the extra data is lost. If the file previously was shorter, it's extended, and the extended

Part reads as null bytes (' + ').

/* If the original file is larger than the specified size, the excess data is lost. If the original file is smaller, it will be enlarged and the enlarged part read as a null character */

The file offset is not changed.

/* file pointer does not change */

If the size changed, then the St_ctime and St_time fields for the file is update, and the Set-usr-id and Set-group-id PE Rmission bits May

Be cleared.

/* If the size changes, the St_ctime and St_time members of the file will be updated, Set-usr-id and Set-group-id bits may be cleared */

On success-returned, on Error-1 are returned and errno is set appropriately.

/* successfully returned 0. Failed to return 1 and set the appropriate error number errno*/

With Ftruncate (), the file must is open for writing; With truncate. The file must be writable.

/* To be writable, the file's open mode must contain a write tag */

Simple example:

int main ()

{

struct STAT st;

int fd = open ("B.txt", o_creat| O_RDWR);

Or O_wronly, when the new file size is 0

Ftruncate (fd,10);

To expand a file to 10 bytes

/* Here you can add write code */

Fstat (FD,&ST);

printf ("Size of File is%d", st.st_size);

Close (FD);

Truncate ("B.txt", 5);

Truncate the file to a size of 5 bytes, and the extra 5 bytes will be discarded

Stat ("B.txt", &st);

printf ("Size of File is%d", st.st_size);

return 0;

}

Linux-function-truncate;