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diff --git a/gzopen.3 b/gzopen.3 new file mode 100644 index 00000000..9da647e1 --- /dev/null +++ b/gzopen.3 @@ -0,0 +1,261 @@ +.Dd January 15, 2017 +.Dt GZOPEN 3 +.Os +. +.Sh NAME +.Nm gzopen , +.Nm gzdopen +.Nd open gzip file +. +.Sh LIBRARY +.Lb libz +. +.Sh SYNOPSIS +.In zlib.h +.Ft gzFile +.Fn gzopen "const char *path" "const char *mode" +.Ft gzFile +.Fn gzdopen "int fd" "const char *mode" +. +.Sh DESCRIPTION +Opens a gzip (.gz) file +for reading or writing. +The +.Fa mode +parameter is as in +.Xr fopen 3 +.Po +.Dq rb +or +.Dq wb +.Pc +but can also include a compression level +.Pq Dq wb9 +or a strategy: +.Sq f +for filtered data as in +.Dq wb6f , +.Sq h +for Huffman-only compression as in +.Dq wb1h , +.Sq R +for run-length encoding as in +.Dq wb1R , +or +.Sq F +for fixed code compression as in +.Dq wb9F . +.Po +See the description of +.Xr deflateInit2 3 +for more information about the +.Fa strategy +parameter. +.Pc \& +.Sq T +will request transparent writing or appending +with no compression +and not using the gzip format. +. +.Pp +.Dq a +can be used instead of +.Dq w +to request that the gzip stream +that will be written +be appended to the file. +.Dq + +will result in an error, +since reading and writing +to the same gzip file +is not supported. +The addition of +.Dq x +when writing will create the file exclusively, +which fails if the file already exists. +On systems that support it, +the addition of +.Dq e +when reading or writing +will set the flag to close the file on an +.Xr execve 2 +call. +. +.Pp +These functions, +as well as +.Xr gzip 1 , +will read and decode +a sequence of gzip streams in a file. +The append function of +.Fn gzopen +can be used to create such a file. +.Po +Also see +.Xr gzflush 3 +for another way to do this. +.Pc \& +When appending, +.Fn gzopen +does not test whether the file begins with a gzip stream, +nor does it look for the end of the gzip streams +to begin appending. +.Fn gzopen +will simply append a gzip stream +to the existing file. +. +.Pp +.Fn gzopen +can be used to read a file which is not in gzip format; +in this case +.Xr gzread 3 +will directly read from the file without decompression. +When reading, +this will be detected automatically +by looking for the magic two-byte gzip header. +. +.Pp +.Fn gzdopen +associates at +.Vt gzFile +with the file descriptor +.Fa fd . +File descriptors +are obtained from calls like +.Xr open 2 , +.Xr dup 2 , +.Xr creat 2 , +.Xr pipe 2 +or +.Xr fileno 3 +.Po +if the file has been previously opened with +.Xr fopen 3 +.Pc . +The +.Fa mode +parameter is as in +.Fn gzopen . +. +.Pp +The next call of +.Xr gzclose 3 +on the returned +.Vt gzFile +will also close the file descriptor +.Fa fd , +just like +.Xr fclose 3 . +If you want to keep +.Fa fd +open, +use +.Li "fd = dup(fd_keep); gz = gzdopen(fd, mode)" . +The duplicated descriptor should be saved +to avoid a leak, +since +.Fn gzdopen +does not close +.Fa fd +if it fails. +If you are using +.Xr fileno 3 +to get the file descriptor from a +.Vt FILE * , +then you will have to use +.Xr dup 2 +to avoid double-closing +the file descriptor. +Both +.Xr gzclose 3 +and +.Xr flcose 3 +will close the associated file descriptor, +so they need to have different file descriptors. +. +.Sh RETURN VALUES +.Fn gzopen +and +.Fn gzdopen +return +.Dv NULL +if the file could not be opened, +if there was insufficient memory +to allocate the +.Vt gzFile +state, +or if an invalid +.Fa mode +was specified +.Po +an +.Sq r , +.Sq w , +or +.Sq a +was not provided, +or +.Sq + +was provided +.Pc , +or if +.Fa fd +is -1. +The file descriptor +is not used until the next +gz* read, write, seek, or close operation, +so +.Fn gzdopen +will not detect if +.Fa fd +is invalid +.Po +unless +.Fa fd +is -1 +.Pc . +.Va errno +can be checked +to determine if the reason +.Fn gzopen +failed was that the file +could not be opened. +. +.Sh ERRORS +The +.Fn gzopen +function may fail and set +.Va errno +for any of the errors specified +for the routine +.Xr fopen 3 . +. +.Sh SEE ALSO +.Xr deflateInit2 3 , +.Xr fopen 3 , +.Xr gzbuffer 3 , +.Xr gzclose 3 , +.Xr gzdirect 3 , +.Xr gzeof 3 , +.Xr gzerror 3 , +.Xr gzflush 3 , +.Xr gzgetc 3 , +.Xr gzgets 3 , +.Xr gzoffset 3 , +.Xr gzprintf 3 , +.Xr gzputc 3 , +.Xr gzputs 3 , +.Xr gzread 3 , +.Xr gzseek 3 , +.Xr gzsetparams 3 , +.Xr gzwrite 3 +. +.Sh HISTORY +This manual page was converted from +.In zlib.h +to mdoc format by +.An June McEnroe Aq Mt june@causal.agency . +. +.Sh AUTHORS +.An Jean-loup Gailly Aq Mt jloup@gzip.org +.An Mark Adler Aq Mt madler@alumni.caltech.edu |