How to input multi-word string in C

Question

I have this program. I want to input multi-word strings in a 2-D array. But instead of input whole string in first array of 2-D array this program inputs the first three words of my String in the first three array each(as I defined the no of rows in my 2-D array). Here is the program:

int main()
{
char title[50];
int track;
int question_no;

printf("\nHow many questions?\t");
scanf("%d",&question_no);
track=0;
char question[question_no][100];
while(track<=question_no)
    {
        printf("Question no %d is:",track+1);
        scanf("%s",question[track]);
        printf("Q %d.%s",track,question[track]);
        track++;
    }
}

Here "question_no" is the no of strings I want to input in my 2-D array- "question". But when I input first string, the string's first three words get inputted in the three arrays of 2-D array. It even doesn't ask me to input 2nd or 3rd strings.

A solution to this problem, as I perceive, should be 3-D array. Because that way 2-D arrays inside the outermost array would print the whole multi-word string (But there too I am bound to the length of each string, I think). If this, 3-D array concept, can solve the problem, then is there some efficient method also? Which is better, faster and less time consuming than 3-D array method.

paxdiablo · Accepted Answer · 2013-11-19 07:29:26Z

2

scanf("%s") will scan a string up to the first piece of white space it finds, hence it's unsuitable for multi-word input.

There are ways to use scanf for line-based input but you're generally better off using methods that are easier to protect from buffer overflow, such as an old favorite of mine:

#include <stdio.h>
#include <string.h>

#define OK       0
#define NO_INPUT 1
#define TOO_LONG 2
static int getLine (char *prmpt, char *buff, size_t sz) {
    int ch, extra;

    // Get line with buffer overrun protection.
    if (prmpt != NULL) {
        printf ("%s", prmpt);
        fflush (stdout);
    }
    if (fgets (buff, sz, stdin) == NULL)
        return NO_INPUT;

    // If it was too long, there'll be no newline. In that case, we flush
    // to end of line so that excess doesn't affect the next call.
    if (buff[strlen(buff)-1] != '\n') {
        extra = 0;
        while (((ch = getchar()) != '\n') && (ch != EOF))
            extra = 1;
        return (extra == 1) ? TOO_LONG : OK;
    }

    // Otherwise remove newline and give string back to caller.
    buff[strlen(buff)-1] = '\0';
    return OK;
}

This is a handy routine which provides line-based input, buffer overflow protection, detection of lines that are too long, cleaning up of those lines so that they don't affect the next input operation and prompting.

A test program can be seen below:

int main (void) {
    int rc;
    char buff[10] = "";

    while ( 1) {
        rc = getLine ("\nWhat? ", buff, sizeof(buff));
        if (rc == NO_INPUT) {
            // Extra NL since my system doesn't output that on EOF.
            printf ("\nNo input\n");
            return 1;
        }

        if (rc == TOO_LONG) {
            printf ("Input too long [%s]\n", buff);
            continue;
        }

        if ( strcmp (buff, "exit") == 0)
            break;
        printf ("OK [%s]\n", buff);
    }

    return 0;
}

And a transcript follows:

pax> ./testprog

What? hello
OK [hello]

What? this is way too big for the input buffer
Input too long [this is w]

What? 
OK []

What? exit

pax> _

edited Nov 19, 2013 at 7:29

answered Nov 19, 2013 at 6:43

paxdiablo

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2 Comments

Ashish Tomer Over a year ago

I am a beginner so I am unable to understand. But I have saved it in .pdf for future learning. :)

Ashish Tomer Over a year ago

Thank you @paxdiablo You are a real pro. I am learning now from you people.

Raiyan · Accepted Answer · 2013-11-19 06:44:16Z

1

Use gets(), this takes input as one string including white spaces, even the newline. But will take in till the first newline. As opposed to scanf(), which takes upto the first white space.

answered Nov 19, 2013 at 6:44

Raiyan

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2 Comments

Daniel Over a year ago

Except gets() should never be used, since it has no buffer overflow protection. Use fgets() and you're all good.

Ashish Tomer Over a year ago

fgets() . . Hmmmm! That was good suggestion @Daniel Thanks! :)

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