// simple examples of const - invalid statements are commented out
#include <stdio.h>
int main()
{
char *s = "hello S"; // "hello S" is a constant, s is pointed at it
char a[30] = "hello A"; // define an array, initialise it with characters "hello A"
printf("s = %s a = %s\n", s, a);
//*(s+2) = 'X'; // error! change third element of char* pointed to by s
// would give run time segmentation error
a[2] = 'X'; // change third element of array a
printf("s = %s a = %s\n", s, a);
s=a; // point s at array a
*(s+2) = 'Z'; // change third element of char* pointed to by , i.e. a[2]
printf("s = %s a = %s\n", s, a);
// define pointer s1 to a constant char*, we cannot change the char* s1 points at
const char *s1 = "hello"; // pointer to a constant char*
//*s1='X'; // compile time error! - assignment of read-only location
s1=a; // but we can point s1 at array a
//*s1='X'; // compile time error! - although s1 points at a (which can be written)
// compiler still gives assignment of read-only location
// define pointer s2 a constant pointer to char*
char *const s2 = a; // constant pointer to char *, initialised to point to a
*s2='Q'; // change a[0]
printf("s2 = %s a = %s\n", s2, a);
//s2=a; // compile time error! - assignment of read-only location
// cannot change what s2 points at
// define pointer s3 to a constant pointer to constant char*
const char *const s3 = a; // constant pointer to const char *, initialised to point to a
printf("s3 = %s a = %s\n", s3, a);
getchar();
}
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