How to get the size of a const char pointer

Question

const char *array[] = {"ax","bo","cf"};

tried

printf("size of array = %lu\n", sizeof(const char*));

result != 3

also

printf("size of array = %lu\n", sizeof(array));
result != **DESIRED ANSWER** = 4

NOTE... I have read related questions on here but none had a relation with my question......

Solution 1

To get the size of a const char pointer:`

printf("%zu\n", sizeof(const char *));

To get the size of the array array[]:

const char *array[] = {"ax","bo","cf"};
printf("%zu\n", sizeof array);

To get the number of elements in the array array[], divide the size of the array by the size of an array element.

const char *array[] = {"ax","bo","cf"};
// Size of array/size of array element
printf("%zu\n", sizeof array / sizeof array[0]); 
// expect 3

Solution 2

anyType array[3] = {};    

sizeof(array[0]) //will return the size of one element of any array

sizeof(array) //will return the storage requirement of the entire array

(sizeof(array)/sizeof(array[0])) //will return the number of elements in the array

But remember that sizeof() resolves at compile time so it only works if you have the actual array variable, not a pointer to an element. Meaning you can't pass the array into a function and then take the sizeof() of the passed parameter unless you declare the parameter to be an array of fixed size.

Solution 3

you need to first find out the size of const char * then you need to divided by this to size of you array like this :

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

int main()
{
    const char *array[] = {"ax","bo","cf"};
    printf("%d",sizeof(array)/sizeof(const char*));
    return 0;
}

Comments

[RoadRunner]

Just out of curiosity, which is clearer? sizeof array / sizeof array[0] or sizeof array / sizeof *array. BTW I think the third example has typo. Should be array instead of a.

[chux - Reinstate Monica]

@RoadRunner Which is best sizeof array / sizeof array[0] or sizeof array / sizeof *array is easy. Every group should employ a coding style that settles style issues like this and then use the agreed upon one. I prefer [] at it emphasizes the array nature of the object.

[chux - Reinstate Monica]

@RoadRunner I avoid the sizeof array/sizeof(const char*) style as that is harder to code, review and maintain. To know the type is correct requires cross checking with the declaration. This is especial a nuisance when the type is defined in a field of some structure located in a header file.

[chux - Reinstate Monica]

"sizeof() resolves at compile time " --> sizeof also applies to variable length arrays, a run-time determination.

[bd2357]

Good point on variable arrays, There is also the issue of an expression with side effects as parameter to sizeof which must be evaluated. But this is such a bad practice I don't think I have ever seen it in the wild.