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int main (int argc, const char * argv[])

{

char x = '!'; // The character '!'

while (x <= '~') { // The character '~'

printf("%x is %c\n", x, x);

x++;

}

return 0;

}

Build it and run it.

The non-printable characters can be expressed using escape sequences that start with \. You’ve already used \n for the newline character. Here are some common ones:

Table 34.1 Common escape sequences

\n new line

\t tab

\' single-quote

\" double-quote

\0 null byte (0x00)

\\ backslash

char *

A C string is just a bunch of characters right next to each other in memory. The string ends when the character 0x00 is encountered.

Figure 34.1 The word “Love” as a C string

Functions that take C strings expect the address of the string’s first character. strlen(), for example, will count the number of characters in a string. Try building a string and using strlen() to count the letters:

#include // For printf

#include // For malloc/free

#include // For strlen

int main (int argc, const char * argv[])

{

char x = '!'; // The character '!'

while (x <= '~') { // The character '~'

printf("%x is %c\n", x, x);

x++;

}

// Get a pointer to 5 bytes of memory on the heap

char *start = malloc(5);

// Put 'L' in the first byte

*start = 'L';

// Put 'o' in the second byte

*(start + 1) = 'o';

// Put 'v' in the third byte

*(start + 2) = 'v';

// Put 'e' in the fourth byte

*(start + 3) = 'e';

// Put zero in the fifth byte

*(start + 4) = '\0';

// Print out the string and its length

printf("%s has %zu characters\n", start, strlen(start));

// Print out the third letter

printf("The third letter is %c\n", *(start + 2));

// Free the memory so that it can be reused

free(start);

start = NULL;

return 0;

}

Build and run it.

Notice the places where you added a pointer and a number together. start is declared to be a char *. A char is one byte. So start + 1 is a pointer one byte further in memory than start. start + 2 is two bytes further in memory than start.

Figure 34.2 The address of each character

This adding to a pointer and dereferencing the result is so common that there is a shorthand for it: start[2] is equivalent to *(start + 2). Change your code to use it:

char *start = malloc(5);

start[0] = 'L';

start[1] = 'o';

start[2] = 'v';

start[3] = 'e';

start[4] = '\0';

printf("%s has %zu characters\n", start, strlen(start));

printf("The third letter is %c\n", start[2]);

free(start);

start = NULL;

return 0;

}

Build and run it.

It should be mentioned that this works with any data type. Here, for example, I can make a list of my favorite 3 floating point numbers and print them out:

int main (int argc, const char * argv[])

{

// Claim a chunk of memory big enough to hold three floats

float *favorites = malloc(3 * sizeof(float));

// Push values into the locations in that buffer

favorites[0] = 3.14158;

favorites[1] = 2.71828;

favorites[2] = 1.41421;

// Print out each number on the list

for (int i = 0; i < 3; i++) {

printf("%.4f is favorite %d\n", favorites[i], i);

}

// Free the memory so that it can be reused

free(favorites);

favorites = NULL;

return 0;

}

The only interesting difference here is that favorites is typed as a float *. A float is 4 bytes. Thus favorites + 1 is 4 bytes further in memory than favorites.

String literals

If you were dealing with C strings a lot, malloc’ing the memory and stuffing the characters in one-by-one would be a real pain. Instead, you can create a pointer to a string of characters (terminated with the zero character) by putting the string in quotes. Change your code to use a string literal:

int main (int argc, const char * argv[])

{

char x = '!'; // The character '!'

while (x <= '~') { // The character '~'

printf("%x is %c\n", x, x);

x++;

}

char *start = "Love";

printf("%s has %zu characters\n", start, strlen(start));

printf("The third letter