Length of array of strings

November 14, 2021

How can we determine the length of an array of strings when we don’t know the length?

For example in this piece of code:

#include <stdio.h>

int main() {
    int n;
    char names[3][10] = { “Alex”, “Phillip”, “Collins” };

    for (n = 0; n < 3; n++)    
        printf(“%s \n”, names[n]);
}

n < 3 is assuming you know the length of the array but how can you determine it’s length when we don’t know?

I have tried a few alternatives such as:

int arraySize() {
    size_t size, i = 0;
    int count = 0;
    char names[3][10] = { “Alex”, “Phillip”, “Collins” };

    size = sizeof(names) / sizeof(char*);

    for (i = 0; i < size; i++) {
        printf("%d - %s\n", count + 1, *(names + i));
        count++;
    }

    printf("\n");
    printf("The number of strings found are %d\n", count);
    return 0;
}

for (n = 0; n < sizeof(names); n++)

but they all error out.

Any help is appreciated.

>Solution :

I am not sure what you mean by they all err out.

There is a syntax issue in the code posted as you use guillemet characters instead of double quotes: “Alex” should be "Alex". This could be a side effect of your cut/paste method to post the code, but nevertheless a potential issue.

Your approach using size = sizeof(names) / sizeof(char*); is right but the type is incorrect: names[0] is not a char *, it is an array of 10 characters. You should use size = sizeof(names) / sizeof(names[0]); which works for all arrays, regardless of the type.

Here is a modified version where the length of the array is determined by the compiler:

#include <stdio.h>

int main() {
    char names[][10] = { "Alex", "Phillip", "Collins" };
    int i, length = sizeof(names) / sizeof(names[0]);

    for (i = 0; i < length; i++)    
        printf("%d: %s\n", i + 1, names[i]);

    return 0;
}

Notes:

you could use size_t instead of int for array length and index variables, but it is only necessary for very large arrays and the printf conversion specifier would be %zu for a value of type size_t.
it is less confusing to use length for the length of an array and reserve size for sizes in bytes obtained from sizeof().