Find the size of a string pointed by a pointer

Question

#include 

int main ()
{
    char *ptr = \"stackoverflow\"

}

Is there any way to find the length of stackoverflow pointed by ptr, a

Answer 1

You can try using:

char *ptr = "stackoverflow"
size_t len = strlen(ptr);

Answer 2

1. sizeof() returns the size required by the type. Since the type you pass to sizeof in this case is a pointer, it will return size of the pointer.

   If you need the size of the data pointed by a pointer you will have to remember it by storing it explicitly.

2. sizeof() works at compile time. so, sizeof(ptr) will return 4 or 8 bytes typically. Instead use strlen.

Answer 3

Even though this is a generic C question, it gets pretty high hits when looking this question up for C++. Not only was I in C/C++ territory, I also had to be mindful of Microsoft's Security Development Lifecycle (SDL) Banned Function Calls for a specific project which made strlen a no-go due to,

For critical applications, such as those accepting anonymous Internet connections, strlen must also be replaced...

Anyway, this answer is basically just a twist on the answers from the others but with approved Microsoft C++ alternative function calls and considerations for wide-character handling in respect to C99's updated limit of 65,535 bytes.

#include <iostream>
#include <Windows.h>
int wmain()
{
    //  1 byte per char, 65535 byte limit per C99 updated standard
    //  https://stackoverflow.com/a/5351964/3543437
    const size_t ASCII_ARRAY_SAFE_SIZE_LIMIT = 65535; 

    //  Theoretical UTF-8 upper byte limit of 6; can typically use 16383 for 4 bytes per char instead:
    //  https://stijndewitt.com/2014/08/09/max-bytes-in-a-utf-8-char/
    const size_t UNICODE_ARRAY_SAFE_SIZE_LIMIT = 10922;

    char ascii_array[] = "ACSCII stuff like ABCD1234.";
    wchar_t unicode_array[] = L"Unicode stuff like → ∞ ∑ Σὲ γνωρίζω τὴν ደሀ ᚦᚫᛏ.";

    char * ascii_array_ptr = &ascii_array[0];
    wchar_t * unicode_array_ptr = &unicode_array[0];

    std::cout << "The string length of the char array is: " << strnlen_s(ascii_array_ptr, ASCII_ARRAY_SAFE_SIZE_LIMIT) << std::endl;
    std::wcout << L"The string length of the wchar_t array is: " << wcsnlen_s(unicode_array_ptr, UNICODE_ARRAY_SAFE_SIZE_LIMIT) << std::endl;

    return 0;
}

Output:

The string length of the char array is: 27
The string length of the wchar_t array is: 47

Answer 4

You are looking for the strlen() function.

Answer 5

if ptr length is an argument of a function it's reasonable to use pointers as a strings. we can get string length by following code:

char *ptr = "stackoverflow";
length=strlen((const char *)ptr);

And for more explanation, if string is an input string by user with variable length, we can use following code:

unsigned char *ptr;
ptr=(unsigned char *)calloc(50, sizeof(unsigned char));
scanf("%s",ptr );
length=strlen((const char *)ptr);

Answer 6

The strlen() function provided by string.h gives you how many "real characters" the string pointed by the argument contains. However, this length does not include the terminating null character '\0'; you have to consider it if you need the length to allocate memory.

That 4 bytes is the size of a pointer to char on your platform.