Question

I have been trying to create an iphone app sending telnet command. However what puzzling me is that the sizes of certain strings are so much different, particularly when they include \n or \r. I listed out a few examples. Please assist.

const char *a = "play 25\n";
int sizeBitA1 = sizeof(a);  // 8 units
int sizeBitA2 = sizeof("play 25\n"); // 9 units
const char *b = "\r\n";
int sizeBitB1 = sizeof(b);  // 8 units
int sizeBitB2 = sizeof("\r\n");  // 3 units

Answer 1

The following code snippet illustrates all the options of using string constants, arrays and pointers, and sizeof and strlen.

const char *a   = "play\n";
const char at[] = "play\n";
int sizeBitA1 = sizeof(a);  // 8 bytes == size of a pointer
int sizeBitA2 = sizeof("play\n"); // 6 bytes, including the trailing '\0'
int sizeBitA3 = sizeof(at); // 6 bytes, including the trailing '\0'
int sizeBitA4 = strlen(a);  // 5 bytes, excluding the trailing '\0'
int sizeBitA5 = strlen("play\n"); // 5 bytes, excluding the trailing '\0'
int sizeBitA6 = strlen(at); // 5 bytes, excluding the trailing '\0'
const char *b = "\r\n";
const char bt[] = "\r\n";
int sizeBitB1 = sizeof(b);  // 8 bytes == size of a pointer
int sizeBitB2 = sizeof("\r\n");  // 3 bytes, including the trailing '\0'
int sizeBitB3 = sizeof(bt);  // 3 bytes, including the trailing '\0'
int sizeBitB4 = strlen(b);  // 2 bytes, excluding the trailing '\0'
int sizeBitB5 = strlen("\r\n");  // 2 bytes, excluding the trailing '\0'
int sizeBitB6 = strlen(bt);  // 2 bytes, excluding the trailing '\0'