ZIP_FILE_EXTRA_FIELD_GET(3) | Library Functions Manual | ZIP_FILE_EXTRA_FIELD_GET(3)

# NAME

`zip_file_extra_field_get`, `zip_file_extra_field_get_by_id` — get extra field for file in zip

# LIBRARY

libzip (-lzip)

# SYNOPSIS

`#include <zip.h>`

const zip_uint8_t *
`zip_file_extra_field_get`(zip_t *archive, zip_uint64_t index, zip_uint16_t extra_field_index, zip_uint16_t *idp, zip_uint16_t *lenp, zip_flags_t flags);

const zip_uint8_t *
`zip_file_extra_field_get_by_id`(zip_t *archive, zip_uint64_t index, zip_uint16_t extra_field_id, zip_uint16_t extra_field_index, zip_uint16_t *lenp, zip_flags_t flags);

# DESCRIPTION

The `zip_file_extra_field_get`() function returns the extra field with index extra_field_index for the file at position index in the zip archive. This pointer should not be modified or free(3)'d, and becomes invalid when archive is closed. If idp is not `NULL`, the integer to which it points will be set to the ID (two-byte signature) of the selected extra field. If lenp is not `NULL`, the integer to which it points will be set to the length of the extra field. Generally speaking, lenp and idp should be passed since only the extra field data is returned (i.e., neither the ID nor the length, if the idp and lenp arguments are not provided).

The following flags are supported:

`ZIP_FL_CENTRAL`
  Return extra fields from the archive's central directory.
`ZIP_FL_LOCAL`
  Return extra fields from the local file headers.
`ZIP_FL_UNCHANGED`
  Return the original unchanged extra fields, ignoring any changes made.

The `zip_file_extra_field_get_by_id`() function returns the extra field with ID (two-byte signature) extra_field_id and index extra_field_index (in other words, the extra_field_index'th extra field with ID extra_field_id) The other arguments are the same as for `zip_file_extra_field_get`().

# RETURN VALUES

Upon successful completion, a pointer to an extra field is returned, or `NULL` if there is no extra field with that extra_field_index for the file with index index. In case of an error, `NULL` is returned and the error code in archive is set to indicate the error.

# ERRORS

`zip_file_extra_field_get`() and `zip_file_extra_field_get_by_id`() fail if:

[`ZIP_ER_NOENT`]
  index is not a valid file index in archive, or extra_field_index is not a valid extra file index (for ID extra_field_id).

# SEE ALSO

libzip(3), zip_file_extra_field_delete(3), zip_file_extra_field_set(3), zip_file_extra_fields_count(3)

# HISTORY

`zip_file_extra_field_get`() and `zip_file_extra_field_get_by_id`() were added in libzip 0.11.

# AUTHORS

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

# CAVEATS

Please note that the extra field IDs 0x0001 (ZIP64 extension), 0x6375 (Infozip UTF-8 comment), and 0x7075 (Infozip UTF-8 file name) can not be read using `zip_file_extra_field_get`() since they are used by libzip(3) internally.

December 18, 2017 | NiH