Sizeof

sizeof

struct {

    int i;

    char c1;

    char c2;

} s1;

struct {

    char c1;

    int i;

    char c2;

} s2;

struct {

    char c1;

    char c2;

    char c3;

} s3;

struct {

    double d;

    char c1;

    char c2;

} s4;

int main()

{

char* cp = "abcdef";

printf("%d\n", sizeof(cp));             
//pointer to char -> 4

char ca[] = "abcdef";

printf("%d\n", sizeof(ca));             
//abcdef + '\0" -> 7

char ca2[100] = "abcdef" ;

printf("%d\n", sizeof(ca2));           
//100

int ia[100];

printf("%d\n", sizeof(ia));              
//100 * 4 -> 400

char* cp2 = (char*) sizeof(100);       

printf("%d\n", sizeof(cp2));              
//4     

printf("%d\n", sizeof(s1));             
//8

printf("%d\n", sizeof(s2));             
//12      

printf("%d\n", sizeof(s3));             
//3        

printf("%d\n", sizeof(s4));             
//12   

return 0;

}

char f() {

return 'c';

}

int main()

{

int a = 0;

printf("%d\n", sizeof(a++) );         
// sizeof integer -> 4

printf("%d\n", a);                            
// 0    (instruction in sizeof won't be executed)

printf("%d\n", sizeof(f()) );            
// 1    (sizeof(function()) returns the size of the return type of the function)

printf("%d\n", sizeof(f) );               
// 1    (same)

}

sizeof vs strlen

#include <stdio.h>

#include <string.h>

int main()

{

    char *m = "abcde";

    printf("%d\n", strlen(m));

    char r[] = "abcde";

    printf("%d\n", sizeof(r));

}

Output:
5
6