Reading numbers from a text file into an array in C

Question

I'm a programming noob so please bear with me.

I'm trying to read numbers from a text file into an array. The text file, "somenumbers.txt" simply holds 16 numbers as so "5623125698541159".

#include <stdio.h>
main()
{

    FILE *myFile;
    myFile = fopen("somenumbers.txt", "r");

    //read file into array
    int numberArray[16];
    int i;

    for (i = 0; i < 16; i++)
    {
        fscanf(myFile, "%d", &numberArray[i]);
    }

    for (i = 0; i < 16; i++)
    {
        printf("Number is: %d\n\n", numberArray[i]);
    }


}

The program doesn't work. It compiles but outputs:

Number is: -104204697

Number is: 0

Number is: 4200704

Number is: 2686672

Number is: 2686728

Number is: 2686916

Number is: 2004716757

Number is: 1321049414

Number is: -2

Number is: 2004619618

Number is: 2004966340

Number is: 4200704

Number is: 2686868

Number is: 4200798

Number is: 4200704

Number is: 8727656

Process returned 20 (0x14) execution time : 0.118 s Press any key to continue.

Solution 1

change to

fscanf(myFile, "%1d", &numberArray[i]);

Solution 2

5623125698541159 is treated as a single number (out of range of int on most architecture). You need to write numbers in your file as

5 6 2 3 1 2 5  6 9 8 5 4 1 1 5 9  

for 16 numbers.

If your file has input

5,6,2,3,1,2,5,6,9,8,5,4,1,1,5,9 

then change %d specifier in your fscanf to %d,.

  fscanf(myFile, "%d,", &numberArray[i] );  

Here is your full code after few modifications:

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

int main(){

    FILE *myFile;
    myFile = fopen("somenumbers.txt", "r");

    //read file into array
    int numberArray[16];
    int i;

    if (myFile == NULL){
        printf("Error Reading File\n");
        exit (0);
    }

    for (i = 0; i < 16; i++){
        fscanf(myFile, "%d,", &numberArray[i] );
    }

    for (i = 0; i < 16; i++){
        printf("Number is: %d\n\n", numberArray[i]);
    }

    fclose(myFile);

    return 0;
}

Solution 3

for (i = 0; i < 16; i++)
{
    fscanf(myFile, "%d", &numberArray[i]);
}

This is attempting to read the whole string, "5623125698541159" into &numArray[0]. You need spaces between the numbers:

5 6 2 3 ...

Solution 4

Loop with %c to read the stream character by character instead of %d.

Solution 5

There are two problems in your code:

• the return value of scanf must be checked
• the %d conversion does not take overflows into account (blindly applying *10 + newdigit for each consecutive numeric character)

The first value you got (-104204697) is equals to 5623125698541159 modulo 2^32; it is thus the result of an overflow (if int where 64 bits wide, no overflow would happen). The next values are uninitialized (garbage from the stack) and thus unpredictable.

The code you need could be (similar to the answer of BLUEPIXY above, with the illustration how to check the return value of scanf, the number of items successfully matched):

#include <stdio.h>

int main(int argc, char *argv[]) {
    int i, j;
    short unsigned digitArray[16];
    i = 0;
    while (
        i != sizeof(digitArray) / sizeof(digitArray[0])
     && 1 == scanf("%1hu", digitArray + i)
    ) {
        i++;
    }
    for (j = 0; j != i; j++) {
        printf("%hu\n", digitArray[j]);
    }
    return 0;
}

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