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Parsing C Command-Line Arguments

Microsoft Specific

Microsoft C startup code uses the following rules when interpreting arguments given on the operating system command line:

  • Arguments are delimited by white space, which is either a space or a tab.

  • A string surrounded by double quotation marks is interpreted as a single argument, regardless of white space contained within. A quoted string can be embedded in an argument. Note that the caret (^) is not recognized as an escape character or delimiter.

  • A double quotation mark preceded by a backslash, \", is interpreted as a literal double quotation mark (").

  • Backslashes are interpreted literally, unless they immediately precede a double quotation mark.

  • If an even number of backslashes is followed by a double quotation mark, then one backslash (\) is placed in the argv array for every pair of backslashes (\\), and the double quotation mark (") is interpreted as a string delimiter.

  • If an odd number of backslashes is followed by a double quotation mark, then one backslash (\) is placed in the argv array for every pair of backslashes (\\) and the double quotation mark is interpreted as an escape sequence by the remaining backslash, causing a literal double quotation 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

Code

// Parsing_C_Commandline_args.c
// ARGS.C illustrates the following variables used for accessing
// command-line arguments and environment variables:
// argc  argv  envp
//

#include <stdio.h>

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\TEST.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

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