The fdopen() function associates a stream with a file descriptor fildes.

The mode argument is a character string having one of the following values:

The meaning of these flags is exactly as specified for the fopen(3C) function, except that modes beginning with w do not cause truncation of the file.

The mode of the stream must be allowed by the file access mode of the open file. The file position indicator associated with the new stream is set to the position indicated by the file offset associated with the file descriptor.

The fdopen() function preserves the offset maximum previously set for the open file description corresponding to fildes.

The error and end-of-file indicators for the stream are cleared. The fdopen() function may cause the st_atime field of the underlying file to be marked for update.

If fildes refers to a shared memory object, the result of the fdopen() function is unspecified.

Upon successful completion, fdopen() returns a pointer to a stream. Otherwise, a null pointer is returned and errno is set to indicate the error.

The fdopen() function may fail and not set errno if there are no free stdio streams.

The fdopen() function may fail if:

EBADF

The fildes argument is not a valid file descriptor.

EINVAL

The mode argument is not a valid mode.

EMFILE

The number of streams currently open in the calling process is either FOPEN_MAX or STREAM_MAX.

ENOMEM

Insufficient space to allocate a buffer.

The number of streams that a process can have open at one time is STREAM_MAX. If defined, it has the same value as FOPEN_MAX.

File descriptors are obtained from calls like open(2), dup(2), creat(2) or pipe(2), which open files but do not return streams. Streams are necessary input for almost all of the Section 3S library routines.

See attributes(5) for descriptions of the following attributes:

creat(2), dup(2), open(2), pipe(2), fclose(3C), fopen(3C), attributes(5)