How to find the size of a string inside a function in C?

Question

Firstly before I explain, here is the code in C:

#include <stdio.h>

void printSize(char* str);

int main()
{
    char a[100] = "StackOverflow";
    printSize(a);
    return 0;
}

void printSize(char* str)
{
    int n = sizeof(str) / sizeof(char);
    printf("%d" ,n);
}

As you can already see, I am trying to get my function to print the value "100" as 100 is the size that I have allocated to my char array a. However I am getting 8 as my answer. Now I know why I am getting 8 here because it's printing the size of the pointer. So my question is, if I can't use this method to print out the value of "100" then how can I find out the memory allocated to a from inside the function?

Thanks

You can't find it with easy methods. Usually what is done is to add another parameter to the function, `int size`, which tells you the size of the array. — atturri, Apr 08 '16 at 06:51
[Finding the length of a Character Array in C](http://stackoverflow.com/q/4180818/995714) — phuclv, Apr 08 '16 at 07:16

score 3 · Accepted Answer · answered Apr 08 '16 at 06:51

3

To get the length of a string you use the strlen function. To get the size of the array you need to pass it as an argument.

When you get the size of a pointer, you get the size of the actual pointer and not what it points to. In your case you seem to be on a 64-bit platform where pointers are 64 bits (8 bytes), then dividing that by sizeof(char) (which is defined to always be 1) you get the value 8.

answered Apr 08 '16 at 06:51

Some programmer dude

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`#include ` for `strlen()`. – jdarthenay Apr 08 '16 at 06:54
Yeah I know about strlen and the reason why I kept getting 8 as an output, however is there anyway to get this to work without adding a third parameter in my function and also not adding a extra int byte in my allocated memory to store the size? – theprogrammer Apr 08 '16 at 07:20
1

@rohitkrishna094 No there's no way. Once an array has decayed to a pointer, all you have is the pointer, and you have lost all semantic information the compiler might have had for the array. – Some programmer dude Apr 08 '16 at 07:27
Oh ok. Thanks for your help. – theprogrammer Apr 08 '16 at 07:28

How to find the size of a string inside a function in C?

1 Answers1