Updated: April 19, 2023 |
Parse options from a command line
#include <unistd.h> int getopt( int argc, char * const argv[], const char * optstring ); extern char * optarg; extern int optind, opterr, optopt;
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The getopt() function is a command-line parser that can be used by applications that follow the Utility Syntax Guidelines described below.
The optind global variable is the index of the next element of the argv[] vector to be processed. The system initializes optind to 1 when the program is loaded, and getopt() updates it when it finishes with each element of argv[]. Reset optind to 1 if you want to use getopt() to process additional argument sets.
The getopt() function returns the next option character from argv that matches a character in optstring, if there's one that matches. If the option takes an argument, getopt() sets the global variable optarg to point to the option argument as follows:
The getopt() function returns -1 and doesn't change optind if:
This function returns -1 after incrementing optind, if:
If getopt() encounters an option character that isn't contained in optstring, it returns the ? character. If it detects a missing option argument, getopt() returns:
or:
and sets optopt to the option character that caused the error.
The getopt() function always prints a diagnostic message to stderr unless opterr is set to 0, or the first character of optstring is a : character.
Utility Syntax Guidelines
The getopt() function may be used by applications that follow these guidelines:
If an option that doesn't have option arguments is repeated, the results depend on the application.
utility_name [-a] [-b] [-c option_argument] [-d|-e] [-foption_argument] [operand…]
Or:
utility_name [-ab] [-c option_argument] [-d|-e] [-foption_argument] [operand…]
Utilities with very complex arguments may be shown as:
utility_name [options] [operand]
All numbers within the allowable range aren't necessarily semantically correct. A standard utility that accepts an option argument or operand that's to be interpreted as a number, and for which a range of values smaller than that shown above is permitted, describes that smaller range along with the description of the option argument or operand. If an error is generated, the utility's diagnostic message indicates that the value is out of the supported range, not that it's syntactically incorrect.
utility_name -f option_argument…[operand…] utility_name [-g option_argument]…[operand…]
indicate that multiple occurrences of the option and its option argument preceding the ellipses are valid, with semantics as indicated in the Options section of the utility. In the first example, each option argument requires a preceding -f and at least one -foption_argument must be given.
See also Guidelines 3,4,5,6,7,9 and 10 in the Base Definitions volume of the IEEE Std.1003.1-2001 Section 12.2, Utility Syntax Guidelines.
One of the following:
#include <unistd.h> #include <stdlib.h> #include <stdio.h> int main( int argc, char* argv[] ) { int c, errflag = 0; while( ( c = getopt( argc, argv, "abt:" ) ) != -1 ) { switch( c ) { case 'a': printf( "apples\n" ); break; case 'b': printf( "bananas\n" ); break; case 't': printf( "tree = %s\n", optarg ); break; case '?': ++errflag; break; } } return EXIT_SUCCESS; }
Safety: | |
---|---|
Cancellation point | Read the Caveats |
Interrupt handler | No |
Signal handler | No |
Thread | No |
A cancellation point may occur when a thread is executing getopt() if the opterr argument is nonzero.