The gzerror() function shall return a string describing the last error to have occurred associated with the open compressed file stream referred to by file. It shall also set the location referenced by errnum to an integer value that further identifies the error.
The gzerror() function shall return a string that describes the last error associated with the given file compressed file stream. This string shall have the format "%s: %s", with the name of the file, followed by a colon, a space, and the description of the error. If the compressed file stream was opened by a call to gzdopen(), the format of the filename is unspecified.
Rationale: Although in all current implementations of libz file descriptors are named "<fd:%d>", the code suggests that this is for debugging purposes only, and may change in a future release.
It is unspecified if the string returned is determined by the setting
LC_MESSAGES category in the current locale.