Download C Programming: Preprocessor, Typedefs, Multi-file Dev, and Makefiles Guide - Prof. Jonatha and more Study notes Computer Science in PDF only on Docsity!
Practical C Issues:
Preprocessor Directives, Typedefs, Multi-file Development, and Makefiles
Jonathan Misurda [email protected]
#include
- Copies the contents of the specified file into the current file
- < > indicate to look in a known location for includes
- “ “ indicate to look in the current directory or specified path
#include <stdio.h> #include “myheader.h”
#define
- Textual Symbol Replacements
#define PI 3. #define MAX 10
float f = PI; for(i=0;i<MAX;i++) …
#define Macros
- Textual replacements with parameters:
- Good:
- #define MAX(a, b) (a > b)? a : b
- Not so good:
- #define SWAP(a,b) {int t=a; a=b; b=t;}
#if
- #if
- What does preprocessor know?
- Values of #defined variables
- Constants
Example
#include <stdio.h> int main() { #if 0 printf(“this is not printed\n”); #endif printf(“This is printed\n”); return 0; }
Example 2
#include <stdio.h> #define VERSION 5
int main() { #if VERSION < 5 printf(“this is not printed\n”); #endif printf(“This is printed\n”); return 0; }
#else
#if … #elif … #else … #endif
#ifdef
- #if defined
- Checks to see if a macro has been defined, but doesn’t care about the value
- A defined macro might expand to nothing, but is still considered defined
Example
#include <stdio.h> #define MACRO int main() { #if defined MACRO printf(“this is printed\n”); #endif printf(“This is also printed\n”); return 0; }
#undef
- Undefines a macro: #include <stdio.h> #define MACRO #undef MACRO
int main() { #if defined MACRO printf(“this is not printed\n”); #endif printf(“This is printed\n”); return 0; }
Shortcuts
- #if defined → #ifdef
- #if !defined → #ifndef
Structures
Typedef
typedef struct node { int i; struct node *next; } Node;
Node * head;
Struct with Instance
struct node { int i; struct node *next; } Node;
Function Pointers
#include#include <stdio.h><stdlib.h> typedef void (FP)(int, int); void f(int a, int b) { }^ printf("%d\n",^ a+b) void g(int a, printf("%d\n", int b) ab) { } int main()FP {ar1 = f; FP ar2 = g; ar1(2,3);ar2(2,3); return 0; }
Function Pointers As Parameters
void qsort ( void base , size_t num , size_t size , int (comparator)(const void *, const void *) );
Comparator
int compare_ints(const void *a,const void *b) { int *x = (int *)a; int *y = (int *)b;
return *x ‐ *y; }
Multi-file Development
- Want to break up a program into multiple files
- Easier to maintain
- Multiple authors
- Quicker compilation
- Modularity
Static Local Scope
- Scope: Local
- Lifetime: “Global” (life of program)
void f(…) { static int x; … }
File Scope
- “Global Variables” are actually limited to the file
- extern maybe be used to import variables from other files File A int x;
File B extern int x;
Will refer to the same memory location
Example
a.c int x = 0; int f(int y) { return x+y; }
b.c #include <stdio.h> extern int x; int f(int); int main() { x = 5; printf("%d", f(0)); return 0; }
Compiling
gcc a.c b.c
./a.out 5
Static
a.c static int x = 0; static int f(int y) { return x+y; }
b.c #include <stdio.h> extern int x; int f(int); int main() { x = 5; printf("%d", f(0)); return 0; }
Compiling
gcc a.c b.c
/tmp/cccyUCUA.o(.text+0x6): In function main': : undefined reference tox' /tmp/cccyUCUA.o(.text+0x19): In function main': : undefined reference tof' collect2: ld returned 1 exit status
Header Files
- Usually only contain declarations
- Variables
- Functions
- #defined macros
- Paired with an implementation file
