Best Way to Convert Array of Strings to Array of Int in C

Question

My current problem is to read in an unknown number of integers from stdin. My approach is to use gets() to store the entire line as a char array (char str[50]). I am trying to parse the char array and convert each "string int" to an integer and store in an int array. I tried using strtol (nums[i]=strtol(A, &endptr, 10) where A is the char array. However, endptr doesnt seem to store anything when the rest of the A are also numbers. For example, if A is "8 hello" endptr=hello, but when A is "8 6 4" endptr is nothing.

Is there a better approach? Is this possible with atoi? Any help is greatly appreciated! Thanks!

char A[1000];
long nums[1000];
printf("Enter integers: ");
gets(A);
char *endptr;
int i=0;
while(endptr!=A){
    nums[i]=strtol(A, &endptr, 10);
    i++;
}

Iterate over the arrays and convert each number. What's the problem? Show your code. This is no coding service. — too honest for this site, Sep 13 '16 at 20:26
If A="12 35 78" how would I go about iterating over the char array? I could convert it into "1 2 3 5 7 8" but that's not what I need. — Quinn Tai, Sep 13 '16 at 20:37
If there is an invalid input, 1) stop. 2) skip ? e.g. input : `12 hello 34`, get {12} or {12, 34} — BLUEPIXY, Sep 13 '16 at 21:23
`while(endptr!=A){` reads an uninitialized variable. Also you keep on calling `strtol` at the start of the string so this will give the same result every time until you overflow buffer of `nums` — M.M, Sep 14 '16 at 05:18

cdlane · Answer 1 · 2016-09-14T03:58:26.017

This should extract the (positive) integers and skip right over anything else that's not an integer:

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

char string[1024];
long numbers[512]; // worst case ~ 1/2 number of chars = "1 1 1 1 1 1 ... 1"

/* ... */

printf("Enter integers: ");
fgets(string, sizeof(string), stdin);

char *endptr, *ptr = string
int count = 0;

while (*ptr != '\0') {
    if (isdigit(*ptr)) {
        numbers[count++] = strtol(ptr, &endptr, 10);
    } else {
        endptr = ptr + 1;
    }

    ptr = endptr;
}

Best Way to Convert Array of Strings to Array of Int in C

1 Answers1