Difference between revisions of "C language"

Revision as of 02:03, 23 January 2011

Things to remember about the C language if you want to keep sane

The stack

Symptoms:

• The program counter seems to jump around at random
• Corrupted variables and data.

Declarations

#define

volatile

The volatile keyword tells the compiler that the dollowing object is subject to sudden change in a way that is not described in the source code. For example a RS-232 data register that receive data from the outside. Volatile forces the compiler to generate the code that access the memory location each time instead of cache it in a register. Can be applied to any declaration.

Symptoms of missing volatile statements:

• Code fails when you enable compiler optimizations
• Code fails when interrupts or DMA/Hardware peripherials are enabled

extern

static

const

Read only. Can be applied to any declaration.

const volatile unsigned long int base_address = 0xFFFF;

Loop constructs

for() direction and signed while do while

switch(var)
{
	case 0:
	//code
	break;
}

if else

& | ^ ~

Shifts

• Right shift >> The effect on signed numbers is implementation defined, arithmetic shift (ASR) on ARM compilers.
• Left shift <<
• Rotate
  • ROR for unsigned int can be implemented as r0 = ((r0 >> n) | (r0 << (32 - n)));
  • ROL for unsigned int can be implemented as r0 = ((r0 << n) | (r0 >> (32 - n)));

&& || ==

!= > < >= <=

+= -=

• =

/= >>= <<=

Type specifiers

Data types (ARM C and C++)

• char 8 bits
• short 16 bits
• int 32 bits
• long 32 bits
• long long 64 bits (The low word of a long long is at the low address in little-endian mode, and at the high address in big-endian mode.)
• float 32 bits
• double 64 bits
• long double 64 bits
• All pointers 32 bits
• bool (C++ only) 32 bits

Memory alignement in bits is word length or 32 whichever is smallest

Other

• void
• signed
• unsigned

type casting subroutines void return global vs local

pointers

& (unsigned int *)

arrays multiple dimensions array pointers, 1d, 2d string, terminating character /n /r /t escape characters vs ""

character and on what type of lines is belongs on

include files "file" <file> .c .h included libraries