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Basic C language

Basic C

For C, generally a two part process of compiling source files(.c) to object files(.o), then linking the .o files into executables.

C Pre-Processor(CPP)

  • C source files first pass through “macro preprocessor”, before compiler sees code
  • CPP commands begins with “#”
    • #include “file.h” // Inserts file.h into output
    • #include // Looks for file in standard location
    • define M_PI 3.14 // Define constant
    • #if / #endif // Conditional inclusion of text

Structs in C

typedef struct{
    int length_in_seconds;
    int year_recorded;
}Song

Switch

switch(expressions){
    case const1: statements
    case const2: statements
        default: statements
}

What evaluates to FALSE in C

  • 0(integer)
  • NULL(a special kind of pointer that is also 0: more on this later)
  • No explicit Boolean type in old-school C
    • Often u see #define bool (int)
    • Then #define false 0
    • Alternative approach: include a header file #include to provide a boolean type
  • Basically anything where all the bits are 0 is false

Our Tip of the Day.. Valgrind

  • Valgrind
  • Use a <= instead of a < in initializing an array in a completely different part of the program.

Types of Pointers

  • *void ** is a type that can point to anything

  • Use *void ** sparingly to help avoid programs bugs, and security issues, and other bad thing

  • U can have pointers to pointers

  • U can even have pointers to functions…

    int (*fn)(void *,void *) = &foo
// fn is a function that accepts two void* pointers and returns an int
// and initially pointing to the function foo
// (*fn)(x,y) will then call the function

More C Pointer Dangers

  • Declaring a pointer just allocates space to hold the pointer-it does not allocate the thing being pointed to.
  • Local variables in C are not initialized, they may contain anything.