3.6  Quelques révisions 2/3

• De l’utilité du vide :

   
  #include <stdio.h>
  #include <string.h>
  #ifdef PROTOTYPE_INCOMPLET
  int f();
  #endif
  #ifdef PROTOTYPE_COMPLET
  int f(void);
  #endif
  int main(void){
  printf("%d\n",f("abc"));
  return 0;
  }
  int f(void){ return 42; }
  

   
  $ gcc -std=c99 -Wall void.c -o void
  void.c: In function ‘main’:
  void.c:10:1: warning: implicit declaration of function ‘f’ [-Wimplicit-function-declaration]
  $ gcc -Wall -DPROTOTYPE_INCOMPLET void.c -o void
  $ gcc -Wall -DPROTOTYPE_COMPLET void.c -o void
  void.c: In function ‘main’:
  void.c:10:1: error: too many arguments to function 
  

• Les variables globales sont initialisées :

   
  #include <stdio.h>
  int v1;
  int f(void){ static int v2; return v2++; }
  int main(void){
  int v3;
  printf("v1=%d\n",v1);
  printf("v2=%d\n",f());
  printf("encore v2=%d\n",f());
  printf("v3=%d\n",v3);
  return 0;
  }
  

   
  $ gcc -Wall init.c -o init
  init.c: In function ‘main’:
  init.c:9:7: warning: ‘v3’ is used uninitialized in this function [-Wuninitialized]
  $ ./init
  v1=0
  v2=0
  encore v2=1
  v3=-1215623180