By Karl Voelker

• Why know C?
• Syntax
• Memory management
• Strings
• Input and Output

• C is not fun.
• C is not easy.
• C is not pretty.

But...

• C is everywhere.
• C explains the quirks of C++.

• Why know C?
• Syntax
• Memory management
• Strings
• Input and Output

C doesn't have classes.

Lots of libraries for C pretend they have classes, without the polymorphism.

C does not have references.

Example:

This struct type is valid in C and C++:

How do we refer to this type?

For example:

This works in C and C++, but is more common in C:

typedef makes the anonymous struct have the typename foo.

• Why know C?
• Syntax
• Memory management
• Strings
• Input and Output

Memory management isn't much different in C:

Note: in C, the allocated memory is not initialized.

In C, allocating arrays is often necessary.

Note: in C, the array is not initialized.

• Why know C?
• Syntax
• Memory management
• Strings
• Input and Output

• C doesn't have a string class, so we use character arrays.
• We'll still call them "strings."
• Literal strings are made with "".
• Strings always end with \0.
  • Literal strings end with \0 implicitly.

These are from string.h.

char * alice = "alice";
char * bob = "bob";
char * eve = "eve";

strlen(alice) == 5;
strlen(bob) == 3;

strcmp(alice, bob) == -1;
strcmp(bob, bob) == 0;
strcmp(eve, bob) == 1;

char * alice = "alice";

char * clone = malloc(sizeof(char) * 
	(strlen(alice) + 1));
strcpy(clone, alice);

char * twins = malloc(sizeof(char) * 
	(2 * strlen(alice) + 1));
twins[0] = '\0';
strcat(twins, alice);
strcat(twins, alice);

char * alice = "alice";
char * bob = "bob";
char * lice = "lice";

strchr(alice, 'o') == NULL;
strchr(alice, 'c') == alice + 3;

strstr(alice, bob) == NULL;
strstr(alice, lice) == alice + 1;

char * tokens = "foo@bar";

char * first = strtok(tokens, "@");
first == tokens;
strcmp(first, "foo") == 0;

char * second = strtok(NULL, "@");
second == tokens + 4;
strcmp(second, "bar") == 0;

strtok(NULL, "@") == NULL;

char * alice = "alice";
char * zero = "0";
char * hacker_alice = "41ic3";
char * five = "5";
char * six = "   6";
char * seven = "7 + 3";

atoi(alice) == 0;
atoi(zero) == 0;
atoi(hacker_alice) == 41;
atoi(five) == 5;
atoi(six) == 6;
atoi(seven) == 7;

• Why know C?
• Syntax
• Memory management
• Strings
• Input and Output

C does not have cin or cout.

We use scanf and printf, which are functions.

The "format string" tells printf how to print its other arguments.

printf("Hello, World!\n");

char * name = "Alice";
printf("Hello, %s!\n", name);

int hour = 7;
printf("It is %d o'clock.\n", hour);

printf("Hello, %s, it is %d o'clock.\n", 
	name, hour);

fprintf(FILE*, const char*, ...)

Print to a file

sprintf(char*, const char*, ...)

Print to a buffer

snprintf(char*, size_t, const char*, ...)

Print safely to a buffer (extra parameter is buffer size)

The scanf family of functions work like printf, but for input:

int i, j;
scanf("%d%d", &i, &j);

fopen

Open a file

fclose

Close a file

feof

Test for end-of-file

ferror

Test for errors

On UNIX-like systems, manual pages should exist for all standard C functions.

Also, try http://cppreference.com/ , great for C and C++.

Questions?