Representing Programs
Each byte represents some text character in the program. Most modern systems represent text characters using the ASCII standard that represents each character with a unique byte-sized integer. This holds true for our hello.c program. Each byte has an integer value that corresponds to some character.
Text: # i n c l u d e
ASCII Value: 35 105 110 99 108 117 100 101
Hex Value: 23 69 6e 63 6c 75 64 65Files such as our hello.c program file that contain exclusively ASCII characters are known as text files, all other files are known as binary files.
To view the bytes of a program (as hex) you can use the command hexdump [filename]. For example, to view the bytes of hello.c, type hexdump hello.c in the terminal. To see the corresponding ASCII characters, you can use the -C flag. Here is the full output of hexdump -C hello.c. Keep in mind 2 hex digits is 8 binary digits (that is 1 byte). Note that hex is much easier for us as humans to look at than binary.
Offset Bytes as Hex Bytes as ASCII
-------- ------------------------------------------------ ------------------
00000000 23 69 6e 63 6c 75 64 65 20 3c 73 74 64 69 6f 2e #include <stdio.
00000010 68 3e 0a 0a 69 6e 74 20 6d 61 69 6e 28 29 7b 0a h>..int main(){.
00000020 20 20 20 20 70 72 69 6e 74 66 28 22 48 65 6c 6c printf("Hell
00000030 6f 20 57 6f 72 6c 64 5c 6e 22 29 3b 0a 20 20 20 o World\n");.
00000040 20 72 65 74 75 72 6e 20 30 3b 0a 7d 0a return 0;.}.
0000004dA special characters worth pointing out in the hexdump shown is the hex value 0x0a. In the ASCII it appears as a . however it is representing a newline.