C Notes

gcc compiler

-g – option adds debug symbols

An Introduction to GCC – How the compiler works

The sequence of commands executed by a single invocation of GCC consists of the following stages:

preprocessing (to expand macros)
compilation (from source code to assembly language)
assembly (from assembly language to machine code)
linking (to create the final executable)

Compilation is a multi-stage process involving several tools, including the GNU Compiler itself (through the gcc or g++ frontends), the GNU Assembler as, and the GNU Linker ld. The complete set of tools used in the compilation process is referred to as a toolchain.

Variable Scopes

Orange – Global Scope
White – Fine Grained Scope
Pink / yellow – Local Scope

`static` keyword

Global Variable

Scopes variables and function to be local to the file they are contained in. They can not be access and named could be duplicated between files.

Local Variable

Remembers value set between function calls. Variable value is not destroyed at the end of a function like it normally would be

Header files

Include guard

Protects against a header file being loaded twice

#ifndef _EXAMPLE_H_INCLUDED_
/* File contents */
#define _EXAMPLE_H_INCLUDED_
#endif /* end _EXAMPLE_H_INCLUDED_ */

Variables

Volatile

Embed with Elliot: The Volatile Keyword | Hackaday

Tells the compiler to not optimize a variable out and they it could change at any point in time.

volatile uint32_t blah;

Useful for global variables.
Should also be used when declaring variable for loops that are only used for delays

volatile uint8_t i;
for (i=0; i < 200; i++) {
	;
}

Constant

Makes a variable unchangable variable must have a value set at declarations

const float blah = 2.45

Integers

The header file stdint.h that comes with your compiler defines a bunch of integer types that tell you how big they are and if they are signed or not. Our first bit of C code looks like this:

#include < stdint.h >
uint32_t unsigned32BitInteger;

Floating point

In IEEE 754, the float data type, also known as single precision, is a 32-bit value that gives you a range of ±1.18×10−38 to ±3.4×1038 and about 7 digits of precision. That means that you can only accurately represent pi as 3.141592. That’s fewer digits than you might expect.

Not good enough for you? Well the double data type, also known as double precision is a 64-bit value with a range of ±2.23×10−308 to ±1.80×10308 and almost 16 digits of precision. Our value of pi can be 3.141592653589793.

typedef float float32_t;
typedef double float64_t;

Floating point constants are assumed to be doubles (64-bit).

typedef

used to define a new type

typedef struct {
    int x;
    int y;
} point;

point p;

Strings

Strings (c and c++)

Structures

struct point {
    int x;
    int y;
}

struct point p;
p.x = 10;
p.y = 5;
draw(p);

To assign a value to a element in a structure use

structure.element = value

Structure and Pointers

(*structure).element – De-reference element in struct pointer

&(*structure).ptr_element – de-reference address of pointer element in struct pointer

When using a pointer to a structure, to access the members of a structure, you must use the -> operator as follows:

struct_pointer->title;

enum

typedef enum {
    CAN_250000_BAUD = 0,
    CAN_500000_BAUD = 1,
    CAN_1000000_BAUD = 2,
} CAN_BAUD_T;

Control flow and logic

Loop directives

break – breaks out of a loop

continue – skip to next run

Switch / Case

switch (var) {
   case value1:   // note the colon after the case value
      statement;
      statement;
   break;

   case value2:
      statement;
      statement;
   break;

   default:
      statement;
      statement;
   break;
}

Conditional operator

Operator: Conditional

Symbol: ?:

Form: c ? x : y

Operation: If c is nonzero (true) then evaluate x, otherwise evaluate y

The conditional operator (?:) (also known as the “arithmetic if” operator) is C++’s only ternary operator (it takes 3 operands). Because of this, it’s also sometimes referred to as the “ternary operator” (we suggest you avoid calling it this in case C++ adds another ternary operator in the future).

The ?: operator provides a shorthand method for doing a particular type of if/else statement.

If/else statements in the following form:

if (condition)
    expression;
else
    other_expression;

can be rewritten as:

(condition) ? expression : other_expression;

Pointers and memory allocation

Pointers (c and c++)

#coding/c #7-notes