7.5.1 Standard file descriptors ¶

There are three descriptors, however, which are automatically opened when the program starts executing and automatically closed when the program finishes. These are:

Constant: int stdin ¶

File descriptor associated with the standard input. Its value is 0.

Constant: int stdout ¶

File descriptor associated with the standard output. Its value is 1.

Constant: int stderr ¶

File descriptor associated with the standard error. Its value is 2.

7.5.2 Opening and closing files ¶

Procedure: fopen = (string pathname, bits flags) int ¶

Open the file specified by pathname. The argument flags is a combination of file o flags as defined below. If the specified file is successfully opened while satisfying the constraints implied by flags then this procedure yields a file descriptor that is used in subsequent I/O calls to refer to the open file. Otherwise, this procedure yields -1. The particular error can be inspected by calling the errno procedure.

Procedure: fclose = (int fd) int ¶

Close the given file descriptor, which no longer refers to any file. This procedure yields zero on success, and -1 on error. In the later case, the program can look at the particular error by calling the errno procedure.

7.5.3 Creating files ¶

Procedure: fcreate = (string pathname, bits mode) int ¶

Create a file with name pathname. The argument mode is a bits value containing a bit pattern that determines the permissions on the created file. The bit pattern has the form 8rUGO, where U reflects the permissions of the user who owns the file, U reflects the permissions of the users pertaining to the file’s group, and O reflects the permissions of all other users. The permission bits are 1 for execute, 2 for write and 4 for read. If the file is successfully created then this procedure yields a file descriptor that is used in subsequent I/O calls to refer to the newly created file. Otherwise, this procedure yields -1. The particular error can be inspected by calling the errno procedure.

7.5.4 Flags for fopen ¶

The following flags can be combined using bit-wise operators. Note that in POSIX systems the effective mode of the created file is the mode specified by the programmer masked with the process’s umask.

Constant: bits file o default ¶

Flag for fopen indicating that the file shall be opened with whatever capabilities allowed by its permissions.

Constant: bits file o rdwr ¶

Flag for fopen indicating that the file shall be opened for both reading and writing.

Constant: bits file o rdonly ¶

Flag for fopen indicating that the file shall be opened for reading only. This flag is not compatible with file o rdwr nor with file o wronly.

Constant: bits file o wronly ¶

Flag for fopen indicating that the file shall be opened for write only. This flag is not compatible with file o rdwr nor with file o rdonly.

Constant: bits file o trunc ¶

Flag for fopen indicating that the opened file shall be truncated upon opening it. The file must allow writing for this flag to take effect. The effect of combining file o trunc and file o rdonly is undefined and varies among implementations.

7.5.5 Getting file properties ¶

Procedure: fsize = (int fd) long long int ¶

Return the size in bytes of the file characterized by the file descriptor fd. If the system entity characterized by the given file descriptor doesn’t have a size, if the size of the file cannot be stored in a long long int, or if there is any other error condition, this procedure yields -1 and errno is set appropriately.

Procedure: lseek = (int fd, long int offset, int whence) long long int ¶

Set the file offset of the file characterized by the file descriptor fd depending on the values of offset and whence. On success, the resulting offset, as measured in bytes from the beginning of the file, is returned. Otherwise, -1 is returned, errno is set to indicate the error, and the file offset remains unchanged. The effects of offset and whence are:

• If whence is seek set, the file offset is set to offset bytes.
• If whence is seek cur, the file offset is set to its current location plus offset.
• If whence is seek end, the file offset is set to the size of the file plus offset.