### 10.6 Reading and writing combinations

The library provides functions for reading and writing combinations to a file as binary data or formatted text.

Function: int gsl_combination_fwrite (FILE * stream, const gsl_combination * c)

  This function writes the elements of the combination c 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_combination_fread (FILE * stream, gsl_combination * c)

  This function reads elements from the open stream stream into the combination c in binary format. The combination c must be preallocated with correct values of n and k since the function uses the size of c 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_combination_fprintf (FILE * stream, const gsl_combination * c, const char * format)

  This function writes the elements of the combination c 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.10 The function returns `GSL_EFAILED` if there was a problem writing to the file.

Function: int gsl_combination_fscanf (FILE * stream, gsl_combination * c)

  This function reads formatted data from the stream stream into the combination c. The combination c must be preallocated with correct values of n and k since the function uses the size of c to determine how many numbers to read. The function returns `GSL_EFAILED` if there was a problem reading from the file.

#### Footnotes

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In versions of the GNU C library prior to the ISO C99 standard, the type modifier `Z` was used instead.