c-cheat-sheet.md

C Cheat Sheet for personal learning paths

C11 Standard

http://www.open-std.org/JTC1/SC22/WG14/

http://www.open-std.org/JTC1/SC22/WG14/www/standards.html#9899

http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1570.pdf

C11 Standard Library Reference

http://www.tutorialspoint.com/c_standard_library/

http://www.cplusplus.com/reference/clibrary/

http://code-reference.com/c

---

Useful links

SlideShare - Deep C

Compiler Explorer

Code Block CPU Execution Time Benchmark

StackOverflow - rdtsc & rdtscp #1

StackOverflow - rdtsc & rdtscp #2

---

C11 valid main() function declaration

SlideShare - Deep C

StackOverflow - What are the valid signatures for C's main() function? [duplicate]

StackOverflow - Standard way to define parameter-less function main() in C

StackOverflow - Must declare function prototype in C? [duplicate]

StackOverflow - Declare main prototype

C11 Standard - 5.1.2.2.1 Program startup - Page 31

Standard Way of function declarations

Main function: int main(void) {}

Other functions: int f() becomes int f(void)

---

C Variable Declaration

StackOverflow - Initializing variables in C

StackOverflow - Deoptimizing a program for the pipeline in Intel Sandybridge-family CPUs

SlideShare - Deep C

When the variable is declared inside a function it is not initialised, and when it is declared in static or global scope it's set to 0:

int a; // is set to 0
void foo() {
  int b;  // set to whatever happens to be in memory there
}

The cost of setting auto variables to 0 would increase the cost of function calls. Memsetting the global data segment to 0 however, is a one time cost, that happens at startup. -> Garbage value -> Compiler translating it to 0 in Debug Mode, just like when it's static int 0;:

int a; // undefined

Standard variables are initialized to 0:

static int a; // 0

Private vs Public Variables:

---

input & output

printf();   // Writes output
putchar();  // Writes output
scanf();    // reads input
getchar();  // reads input

---

int & float

• integer numbers truncate (5 / 9 = 0.55 -> 0. -> 0)!
• floating-point numbers NOT truncate -> Mathematical orders in arithmetic ALWAYS work!

---

Escape Sequences - Complete set

\a    // alert (bell) character
\b    // backspace
\f    // formfeed
\n    // newline
\r    // carriage return
\t    // horizontal tab
\v    // vertical tab
\\    // backslash
\?    // question mark
\’    // single quote
\"    // double quote
\ooo  // octal number
\xhh  // hexadecimal number

Defining Escape Sequences

#define VTAB ’\013’  // ASCII vertical tab
#define BELL ’\007’  // ASCII bell character
#define VTAB ’\xb’   // ASCII vertical tab - hexadecimal
#define BELL ’\x7’   // ASCII bell character - hexadecimal

---

C Data Types

int     // integer -> e.g. 4
float   // floating point -> numbers that may have fractional part e.g. 3.234
char    // character -> a single byte
short   // short integer
long    // long integer
double  // double-precision floating point

---

Output Formatting

%d     // print as decimal integer
%6d    // print as decimal integer, at least 6 characters wide
%f     // print as floating point
%6f    // print as floating point, at least 6 characters wide
%.2f   // print as floating point, 2 characters after decimal point
%6.2f  // print as floating point, at least 6 wide and 2 after decimal point

• Among others, printf() also recognizes %o for octal, %x for hexadecimal, %c for character, %s for character string, and %% for % itself.

---

Symbolic constants

A #define line defines a symbolic name or symbolic constant to be a particular string of characters:

#define   NAME   replacement_text

• any occurrence of name (not in quotes and not part of another name) will be replaced by the corresponding replacement text
• The name has the same form as a variable name: a sequence of letters and digits that begins with a letter
• The replacement text can be any sequence of characters; it is not limited to numbers
• The quantities of NAME are symbolic constants, not variables, so they do not appear in declarations

---

1.5 Character Input and Output

c = getchar();

• Each time it is called, getchar reads the next input character from a text stream and returns that as its value
• Variable c contains the next character of input
• The characters normally come from the keyboard

putchar(c);

• The function putchar prints a character each time it is called, prints the contents of the integer variable c as a character, usually on the screen
• Calls to putchar and printf may be interleaved; the output will appear in the order in which the calls are made

---

1.5.1 File Copying

Given getchar and putchar, you can write a surprising amount of useful code without knowing anything more about input and output. The simplest example is a program that copies its input to its output one character at a time:

read a character
while (character is not end-of-file indicator)
  output the character just read
  read a character

c = getchar();  // scanf("%d", &c);
putchar(c);     // printf("%d", c);