CODEWITHSUNDEEP
carraysstringscanf
Nark
Nark

Reputation: 474

Parsing a string with scanf

I need to get integers from a string that an user enters into the console.

For exemple: I have this string: [1, 2, 3, 4, 5] and I would like to get all of the integers from it. I already tried multiple scanf patterns, such as scanf("%*[^\[]%d,", &a), but nothing worked. I couldn't find anything relevant on Stack Overflow either.

The main problem is that he can enters between 1 and 50 integers into his string. I have no idea about how to stock only integers (removing ',' and '[' ']' ) into an array.

Some solutions have been found for removing special chars such as [ ] or , But now I still need to remove SPACE between comas and integers...

EDIT : problem solved using fgets. I was using scanf to get my string, but it were stopping to SPACES.

Fond out how to do that with scanf :

while(scanf(" %d",&i))

Upvotes: 2

Views: 12193

Answers (3)

RoadRunner
RoadRunner

Reputation: 26335

Using scanf() for parsing strings is not recommended.

Similarly to others answers, you can use strtok to parse the numbers between "[],", and convert the found numbers using strtol. It would be dangerous to use something like atoi() for integer conversion, as their is no error checking with it. Some more error checking with strtol() can be found in the man page.

Here is some sample(can be improved) code which does this:

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

#define MAXNUM 50
#define BASE 10

int main(void) {
    char string[] = "[1,2,3,4,5]";
    char *number, *endptr;
    const char *delim = "[],";
    int numbers[MAXNUM], current;
    size_t i, count = 0;

    number = strtok(string, delim);
    while (number != NULL) {
        current = strtol(number, &endptr, BASE);

        /* checking if valid digit found */
        /* more error checking can be added */
        if (endptr != number) {
            numbers[count++] = current;
        }
        number = strtok(NULL, delim);
    }

    for (i = 0; i < count; i++) {
        printf("numbers[%zu] = %d\n", i, numbers[i]);
    }

    return 0;
}

Sample input 1:

string[] = "[1,2,3,4,5]";

Output 1:

numbers[0] = 1
numbers[1] = 2
numbers[2] = 3
numbers[3] = 4
numbers[4] = 5

Sample input 2:

string[] = "[1,a,3,c,5]";

Output 2:

numbers[0] = 1
numbers[1] = 3
numbers[2] = 5

Upvotes: 0

simon
simon

Reputation: 2164

scanf/sscanf does not support regular expressions. You should try something like:

const char my_string[] = "[1,2,3,4,5]";
int a,b,c,d,e;
sscanf(my_string, "[%d,%d,%d,%d,%d]", &a, &b, &c, &d, &e);

Example: http://ideone.com/AOaD7x

It can also be good to check the return value of scanf/sscanf:

int retval = sscanf(my_string, "[%d,%d,%d,%d,%d]", &a, &b, &c, &d, &e);
if (retval != 5)
    fprintf(stderr, "could not parse all integers\n");

Reference

Edit: In your edited question you asks how to do this if there is a variable number of integers. You can use strchr to locate the next comma in the string and continue to iterate until no more comma is found. This assumes that the string ends with ].

const char my_string[] = "[1,2,3,4,5]";

/* start at first integer */
const char *curr = &my_string[1];

while (curr != NULL) {
    /* scan and print the integer at curr */
    int tmp;
    sscanf(curr, "%d", &tmp);
    printf("%d\n", tmp);

    /* find next comma */
    curr = strchr(curr, ',');

    /* if a comma was found, go to next integer */
    if (curr)
        /* warning: this assumes that the string ends with ']' */
        curr += 1;
}

Example: http://ideone.com/RZkjWN

Upvotes: 3

sameera sy
sameera sy

Reputation: 1718

Try this piece of code, by using strtok you can separate out all type of unwanted characters in your string. Add all your unwanted set of character to this s array and let strtok do the work.

char str[]="[1,2,3,4,5]";
const char s[4] = "[],"; // All unwanted characters to be filtered out
char *token;
token = strtok(str, s);
while( token != NULL ) 
{
  printf( "%d\n", atoi(token));
  token = strtok(NULL, s);
}

Since you have it in the integer format, you could store it in an array and go further with it.

Output : 

1
2
3
4
5

Upvotes: 1

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