— Function: int gsl_permutation_fwrite (FILE * stream, const gsl_permutation * p)

This function writes the elements of the permutation p to the stream stream in binary format. The function returns GSL_EFAILED if there was a problem writing to the file. Since the data is written in the native binary format it may not be portable between different architectures.

— Function: int gsl_permutation_fread (FILE * stream, gsl_permutation * p)

This function reads into the permutation p from the open stream stream in binary format. The permutation p must be preallocated with the correct length since the function uses the size of p to determine how many bytes to read. The function returns GSL_EFAILED if there was a problem reading from the file. The data is assumed to have been written in the native binary format on the same architecture.

— Function: int gsl_permutation_fprintf (FILE * stream, const gsl_permutation * p, const char * format)

This function writes the elements of the permutation p line-by-line to the stream stream using the format specifier format, which should be suitable for a type of size_t. In ISO C99 the type modifier z represents size_t, so "%zu\n" is a suitable format.¹ The function returns GSL_EFAILED if there was a problem writing to the file.

— Function: int gsl_permutation_fscanf (FILE * stream, gsl_permutation * p)

This function reads formatted data from the stream stream into the permutation p. The permutation p must be preallocated with the correct length since the function uses the size of p to determine how many numbers to read. The function returns GSL_EFAILED if there was a problem reading from the file.