I am using sscanf to read user input and save to several outputs. As far as my understanding goes, if I have sscanf(iput, %s %s %s %s, arr[0], arr[1], arr[2], arr[3]) I can have up to 4 items entered, but it does not require 4; meaning I could just put two and arr[2] ad arr[3] would have no value. However, I think I am not understanding something since later when I check the values of arr[2]/arr[3] they are not null, when I thought strings were just initialized with \0. Look at my code please and tell me what the if statement should be checking for I guess.

printf("Enter a command: ");
        char input[20];
        char line[5][20];
        fgets(input, 20, stdin);
        sscanf(input, "%s %s %s %s %s", line[0], line[1], line[2], line[3], line[4]);
....

else {
            int status;
            if(line[4] != NULL) {
                char *args[6];
                args[0] = line[0];
                args[1] = line[1];  
                args[2] = line[2];
                args[3] = line[3];
                args[4] = line[4]; 
                args[5] = NULL;
            if ( fork() == 0 ) {
                execv( args[0], args ); // child: call execv with the path and the args
            }
            else {
                wait( &status );  
            }    

CodePudding user response：

Using the comment Jerry Jeremiah said, instead of changing the declaration to a pointer, I changed the line[x] in the if statement to a pointer and checked for NULL.

CodePudding user response：

scanf will attempt to get everything you asked for. You ask for five, it tries to get five.

sscanf(input, "s s s s s", line[0], line[1], line[2], line[3], line[4]);

Without the specification, it will take as many chars as the user is inclined to submit, thus resulting in a buffer overflow. Bad idea.

I would accept one argument at a time, or take it all as one lump.