ZIP_SET_FILE_COMPRESSION(3) | Library Functions Manual | ZIP_SET_FILE_COMPRESSION(3)

# NAME

`zip_set_file_compression` —
set compression method for file in zip

# LIBRARY

libzip (-lzip)

# SYNOPSIS

`#include <zip.h>`

int
`zip_set_file_compression`(zip_t *archive, zip_uint64_t index, zip_int32_t comp, zip_uint32_t comp_flags);

# DESCRIPTION

The `zip_set_file_compression`() function sets the compression method for the file at position index in the zip archive to comp with the compression method specific comp_flags. The comp is the same as returned by zip_stat(3). For the comp argument, currently only the following values are supported:

`ZIP_CM_DEFAULT`
  default compression; currently the same as `ZIP_CM_DEFLATE`, but flags are ignored.
`ZIP_CM_STORE`
  Store the file uncompressed.
`ZIP_CM_BZIP2`
  Compress the file using the bzip2(1) algorithm.
`ZIP_CM_DEFLATE`
  Deflate the file with the zlib(3) algorithm and default options.
`ZIP_CM_XZ`
  Use the xz(1) algorithm for compression
`ZIP_CM_ZSTD`
  Use the zstd(1) algorithm for compression

NOTE: Only the deflate and store methods can be assumed to be universally supported.

The comp_flags argument defines the compression level. This value is dependent on the compression algorithm. In general, lower numbers mean faster de/compression and higher numbers mean slower de/compression. For `ZIP_CM_BZIP`, `ZIP_CM_DEFLATE`, and `ZIP_CM_XZ` 1 is the fastest compression and 9 the best, 0 chooses the default. For `ZIP_CM_ZSTD` possible values are ZSTD_minCLevel(3) to ZSTD_maxCLevel(3); negative values must be cast to zip_uint32_t.

Further compression method specific flags might be added over time.

The current compression method for a file in a zip archive can be determined using zip_stat(3).

# RETURN VALUES

Upon successful completion 0 is returned. Otherwise, -1 is returned and the error information in archive is set to indicate the error.

# ERRORS

`zip_set_file_compression`() fails if:

[`ZIP_ER_COMPNOTSUPP`]
  Unsupported compression method requested.
[`ZIP_ER_INVAL`]
  index is not a valid file index in archive, or the argument combination is invalid.
[`ZIP_ER_RDONLY`]
  Read-only zip file, no changes allowed.

# SEE ALSO

libzip(3), zip_compression_method_supported(3), zip_stat(3)

# HISTORY

`zip_set_file_compression`() was added in libzip 0.11.

# AUTHORS

Dieter Baron <dillo@nih.at> and Thomas Klausner <wiz@gatalith.at>

February 2, 2023 | NiH