Parsing C command-line arguments
Microsoft C startup code uses the following rules when interpreting arguments given on the operating system command line:
- Arguments are delimited by whitespace characters, which are either spaces or tabs.
- The first argument ( argv[0] ) is treated specially. It represents the program name. Because it must be a valid pathname, parts surrounded by double quote marks ( " ) are allowed. The double quote marks aren't included in the argv[0] output. The parts surrounded by double quote marks prevent interpretation of a space or tab character as the end of the argument. The later rules in this list don't apply.
- A string surrounded by double quote marks is interpreted as a single argument, whether it contains whitespace characters or not. A quoted string can be embedded in an argument. The caret ( ^ ) isn't recognized as an escape character or delimiter. Within a quoted string, a pair of double quote marks is interpreted as a single escaped double quote mark. If the command line ends before a closing double quote mark is found, then all the characters read so far are output as the last argument.
- A double quote mark preceded by a backslash ( \" ) is interpreted as a literal double quote mark ( " ).
- Backslashes are interpreted literally, unless they immediately precede a double quote mark.
- If an even number of backslashes is followed by a double quote mark, then one backslash ( \ ) is placed in the argv array for every pair of backslashes ( \\ ), and the double quote mark ( " ) is interpreted as a string delimiter.
- If an odd number of backslashes is followed by a double quote mark, then one backslash ( \ ) is placed in the argv array for every pair of backslashes ( \\ ). The double quote mark is interpreted as an escape sequence by the remaining backslash, causing a literal double quote mark ( " ) to be placed in argv .
This list illustrates the rules above by showing the interpreted result passed to argv for several examples of command-line arguments. The output listed in the second, third, and fourth columns is from the ARGS.C program that follows the list.
| Command-line input | argv[1] | argv[2] | argv[3] |
|---|
| "a b c" d e | a b c | d | e |
| "ab\"c" "\\" d | ab"c | \ | d |
| a\\\b d"e f"g h | a\\\b | de fg | h |
| a\\\"b c d | a\"b | c | d |
| a\\\\"b c" d e | a\\b c | d | e |
| a"b"" c d | ab" c d |
Example
Code
// ARGS.C illustrates the following variables used for accessing // command-line arguments and environment variables: // argc argv envp // #include int main( int argc, // Number of strings in array argv char *argv[], // Array of command-line argument strings char **envp ) // Array of environment variable strings < int count; // Display each command-line argument. printf_s( "\nCommand-line arguments:\n" ); for( count = 0; count < argc; count++ ) printf_s( " argv[%d] %s\n", count, argv[count] ); // Display each environment variable. printf_s( "\nEnvironment variables:\n" ); while( *envp != NULL ) printf_s( " %s\n", *(envp++) ); return; >
One example of output from this program is:
Command-line arguments: argv[0] C:\MSC\ARGS.EXE Environment variables: COMSPEC=C:\NT\SYSTEM32\CMD.EXE PATH=c:\nt;c:\binb;c:\binr;c:\nt\system32;c:\word;c:\help;c:\msc;c:\; PROMPT=[$p] TEMP=c:\tmp TMP=c:\tmp EDITORS=c:\binr WINDIR=c:\nt
END Microsoft Specific
