th_read man page
th_read, th_write — read and write a file header block from a tar archive
int th_read(TAR *t);
int th_write(TAR *t);
This man page documents version 1.2 of libtar.
The th_read() function reads the next block from the tar archive associated with the TAR handle t. It then sets the current tar header associated with t to the contents of the block read.
The th_write() function writes the contents of the current tar header associated with t to the tar archive associated with t.
On successful completion, th_read() and th_write() will return 0. On failure, they will return -1 and set errno to an appropriate value.
On EOF, th_read() will return 1.
th_read() and th_write() will fail if:
Less than T_BLOCKSIZE blocks were read or written.
th_write(3) is an alias of th_read(3).