notes-sizeof-strlen

migrate from https://cmakerhk.wordpress.com/2018/09/28/sizeof-vs-strlen/

Sizeof()

#include 
int main() 
{ 
    printf("%d\n",sizeof(char)); // output 1
    printf("%d\n",sizeof(int));  // output 4
    printf("%d\n",sizeof(float));// output 4
    printf("%d", sizeof(double));// output 8
    return 0; 
}  

Sizeof will return the size of the variable

#include 
int main() 
{ 
   int arr[] = {1, 2, 3, 4, 7, 98, 0, 12, 35, 99, 14}; 
   printf("Number of elements :%d", sizeof(arr)/sizeof(arr[0])); 
   return 0; 
}  

Number of elements :11

This is useful for getting the number of the elements of an array.

allocate memory dynamically - To allocate block of memory dynamically.

int *ptr = malloc(10*sizeof(int));

strlen()

size_t strlen(const char *str)

not include \0

//========compare

Since strlen() not inlclude \0

// C program to demonstrate difference  
// between strlen() and sizeof() 
#include 
#include 
 
int main() 
{ 
    char str[] = "November"; 
    printf("Length of String is %d\n", strlen(str));  //8
    printf("Size of String is %d\n", sizeof(str));    //9
} 

#include  
#include  
using namespace std; 
 
int main() 
{ 
        char a[] = {"Geeks for"}; 
        char b[] = {'G','e','e','k','s',' ','f','o','r'}; //9 char total
        cout << "sizeof(a) = " << sizeof(a); 
        cout << "\nstrlen(a) = "<< strlen(a); 
        cout<<  "\nsizeof(b) = " << sizeof(b); 
        cout<<  "\nstrlen(b) = " << strlen(b); 
         
        return 0; 
} 

sizeof(a): 10 //include the NULL at the end

strlen(a): 9 // not include the NULL

sizeof(b): 9 // total 9 char ma

strlen(b):11 // abnormal

ref:

https://www.geeksforgeeks.org/sizeof-operator-c/

https://www.tutorialspoint.com/c_standard_library/c_function_strlen.htm

https://www.geeksforgeeks.org/difference-strlen-sizeof-string-c-reviewed/