Find the number of strings in an array of strings in C

Question

char* names[]={"A", "B", "C"};

Is there a way to find the number of strings in the array? For example, in this case it should output: 3.

Answer 1

For an array, which the examples in the bounty are, doing sizeof(names)/sizeof(names[0]) is sufficient to determine the length of the array.

The fact that the strings in the examples are of different length does not matter. names is an array of char *, so the total size of the array in bytes is the number of elements in array times the size of each element (i.e. a char *). Each of those pointers could point to a string of any length, or to NULL. Doesn't matter.

Test program:

#include<stdio.h>

int main(void)
{
    char* names1[]={"A", "B", "C"}; // Three elements
    char* names2[]={"A", "", "C"}; // Three elements
    char* names3[]={"", "A", "C", ""}; // Four elements
    char* names4[]={"John", "Paul", "George", "Ringo"}; // Four elements
    char* names5[]={"", "B", NULL, NULL, "E"}; // Five elements

    printf("len 1 = %zu\n",sizeof(names1)/sizeof(names1[0]));
    printf("len 2 = %zu\n",sizeof(names2)/sizeof(names2[0]));
    printf("len 3 = %zu\n",sizeof(names3)/sizeof(names3[0]));
    printf("len 4 = %zu\n",sizeof(names4)/sizeof(names4[0]));
    printf("len 5 = %zu\n",sizeof(names5)/sizeof(names5[0]));
}

Output:

len 1 = 3
len 2 = 3
len 3 = 4
len 4 = 4
len 5 = 5

EDIT:

To clarify, this only works if you've defined an array, i.e. char *names[] or char names[][], and you're in the scope where the array was defined. If it's defined as char **names then you have a pointer which functions as an array and the above technique won't work. Similarly if char *names[] is a function parameter, in which case the array decays to the address of the first element.

Answer 2

In this case you can divide the total size by the size of the first element:

num = sizeof(names) / sizeof(names[0]);

Careful though, this works with arrays. It won't work with pointers.

Answer 3

It depends on how your array is created. In C, there is no way to check the length of an array that is a pointer, unless it has a sentinel element, or an integer passed with the array as a count of the elements in the array. In your case, you could use this:

int namesLen = sizeof(names) / sizeof(char);

However, if your array is a pointer,

char **names = { "A", "B", "C" };

You can either have an integer that is constant for the length of the array:

int namesLen = 3;

Or add a sentinel value (e.g. NULL)

char **names = { "A", "B", "C", NULL };

int namesLen = -1;
while (names[++namesLen] != NULL) { /* do nothing */}

// namesLen is now the length of your array

As another way, you could create a struct that is filled with the values you want:

struct Array {
    void **values;
    int length;
};

#define array(elements...) ({ void *values[] = { elements }; array_make(values, sizeof(values) / sizeof(void *)); })
#define destroy(arr) ({ free(arr.values); })

struct Array array_make(void **elements, int count)
{
    struct Array ret;
    ret.values = malloc(sizeof(void *) * count);
    ret.length = count;

    for (int i = 0; i < count; i++) {
        ret.values[i] = elements[i];
    }

    return ret;
}

And you would use it as such:

struct Array myArray = array("Hi", "There", "This", "Is", "A", "Test");
// use myArray

printf("%i", myArray.length);
destroy(myArray);

Answer 4

What you're defining here isn't literally an array of strings , it's an array of pointers to characters. if you want to know the number of strings, you simply have to count the pointers, so something like

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

would do,this way you're dividing the size of the array by the size of a single pointer.But be aware this only works if the size of the array is known at compile time(i.e. the array is allocated statically), if it's defined dynamically (i.e. char** strings) then sizeof(strings) would return the size of the pointer not the array.

p.s.:the length of the strings is not relevant, as the array isn't even "aware" of what the pointers point to.

Answer 5

Is there a way to find the number of strings in the array

Of course there is, try this:

#include<stdio.h>

int main(void){
    size_t size, i=0;
    int count=0;
    char* names[]={"A", "B", "C"};

    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;
}

1 - A
2 - B
3 - C

The number of strings found are 3

Same thing with:

#include<stdio.h>

int main(void){
    size_t size, i=0;
    int count=0;
    char *names[]={"Jimmy", "Tom", "Michael", "Maria", "Sandra", "Madonna"};

    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;
}

Output:

1 - Jimmy
2 - Tom
3 - Michael
4 - Maria
5 - Sandra
6 - Madonna

The number of strings found are 6

Or use a Function like this:

#include<stdio.h>

size_t arrLength(size_t len, char **arr){
    size_t i=0;
    size_t count=0;

    for(i=0;i<len;i++){
        printf("%zu - %s\n",count+1, *(arr+i));
        count++;
    }

    return count;
}

int main(void){
    char *names[]={"Jimmy", "Tom", "Michael", "Maria", "Sandra", "Madonna"};
    size_t length,size;

    size = sizeof(names)/sizeof(char*);
    length = arrLength(size, names);

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

Output:

1 - Jimmy
2 - Tom
3 - Michael
4 - Maria
5 - Sandra
6 - Madonna

The number of strings found are 6

Answer 6

int count = sizeof(names)/sizeof(*names);

This takes the total size of names and divides it by the size of one element in names, resulting in 3.

Answer 7

find the number of strings in an array of strings in C

The simple method to find the number of objects in an array is to take the size of the array divided by the size of one of its elements. Use the sizeof operator which returns the object's size in bytes.

// For size_t
#include <stddef.h>

char* names[] = { "A", "B", "C" };
size_t number_of_strings = sizeof names / sizeof names[0];

printf("Number of strings %zu\n", number_of_strings);

Important to consider the type return from sizeof is size_t, an unsigned integer type capable of indexing any array as well as the size of any object. To print a variable of type size_t, use the modifier z.

Answer 8

One simple way to return the number or strings in an array is to iterate over the array until you run out of strings. Here is an example.

#include <stdio.h>

int main()
{
    char* names[] = {"John", "Paul", "George", "Ringo", '\0'};

    int size = 0;
    while(names[++size]!='\0');

    printf("Size: %d\n", size); // Prints "4"

    return 0;
}

This method has the advantage that it works even when the strings are of varying length. Note the terminating NULL byte in the names array, and the ; character to close the while statement as there is no statement body to run.

Answer 9

Making the Array Of Strings to run in a While loop with an Increment Operator, Until the loop becomes NULL, gives the Array Size:

#include<stdio.h>
char* names[]={"A", "B", "C"};

int main(){
int nameSize = 0;
while(names[++nameSize]!='\0');
}

for(i=0;i<nameSize;i++){
printf("%s\n", names[i]);
}

return 0;
}

Output:

A
B
C