Thread: scanf problem

  1. #1
    Registered User
    Join Date
    Sep 2001

    Angry scanf problem

    I'm trying to ask the user for a command and argument like:
    open blah
    would "open" blah. Well. If the user doesn't type an argument, it goes to the next line asking for an argument. Well, this isn't good. Here is the code:
    scanf("%19s 29[^\n]", cmd, arg);
    which didn't work. Here's the other code that I tried:
       for ( j = 0; c = getchar(); j++ ) {
    	if ( c == ' ' ){ i++; j = 0; continue; }
    	if ( c == '\n' ) break;
    	arg[i][j] = c;
    which didn't work. If anyone knows how to do this, please tell me.

  2. #2
    Registered User
    Join Date
    Oct 2001

    int main(void)
    char Cmd[20],Param[30],Temp[10];

    printf("Input command and parameter: ");
    scanf("%19[^ ^\n]%[ \t]%29[^\n]",Cmd,Temp,Param);
    printf("cmd: %s,param: %s\n",Cmd,Param);


  3. #3
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    Don't use scanf - its tricky to stop it reading past a newline

    #include <stdio.h>
    int main ( ) {
        char buff[BUFSIZ];
        while ( fgets(buff,BUFSIZ,stdin) != NULL ) {
            char cmd[100], param[100];
            int res = sscanf( buff, "%s %[^\n]", cmd, param );
            if ( res == 1 ) {
                printf( "command '%s' with no arg\n", cmd );
            } else
            if ( res == 2 ) {
                printf( "command '%s' with arg '%s'\n", cmd, param );
        return 0;
    Gets you
    command 'hello' with no arg
    hello world how are you
    command 'hello' with arg 'world how are you'
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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