Eclipse IDE debugger : step into isn't working properly - c

Question

All the functions used in the main file are correctly defined. However when I try to enter the debugging mode, for some reason IDE isn't stepping into said functions when asked to. Instead it acts like a step over and ignores the lines until the very last line, where out of the blue all variables appear in the window ; prior to that, no variable is present whatsoever.
Here's the main file :
#include "pointers.h"
int main(void){
whatisapointer();
whatisthesizeofapointer();
whatareNpointersplacedsuccessively(6);
return 0;
}
the pointers.c file used to define the functions in main :
#include "pointers.h"
void whatisapointer(){
int *pointer;
pointer = allocateOneInteger();
*pointer = 42;
}
void whatisthesizeofapointer(){
int a = sizeof(char);
int b = sizeof(int);
int c = sizeof(char*);
int d = sizeof(int*);
}
void whatareNpointersplacedsuccessively(int N){
int i, *Npointer, *current;
char *Npointerchar, *currentchar;
Npointer = allocateNInteger(N);
current = Npointer;
current = Npointer+1;
current = Npointer+2;
for(i=0;i<N;i++) *(Npointer+i) = i;
N=2*N;
Npointerchar = allocateNChar(N);
currentchar = Npointerchar;
currentchar = Npointerchar+1;
currentchar = Npointerchar+2;
for(i=0;i<N;i++) Npointerchar[i] = 65+i;
Npointer[N-3] = 0x68676665;
current = Npointer+N-3;
}
int* allocateOneInteger(){
return (int*)malloc(1*sizeof(int));
}
int* allocateNInteger(int N){
return (int*)malloc(N*sizeof(int));
}
char* allocateNChar(int N){
return (char*)malloc(N*sizeof(char));
}
void echange(int a,int b)
{
int temp;
temp=a;
a=b;
b=temp;
}
void echangep(int *pa,int *pb)
{
int temp;
temp=*pa;
*pa=*pb;
*pb=temp;
}
/* Fonction allocateNFloat
*/
void allocateNFloat(int N){
}
And the makefile :
CC := gcc
FLAGS := -g -Wall -Werror
all : prog
prog : pointers.o mainpointers.o
$(CC) pointers.o mainpointers.o -o prog
fonctions.o : pointers.c pointers.h
$(CC) -c pointers.c $(FLAGS) -o pointers.o
mainpointers.o : mainpointers.c pointers.h
$(CC) -c mainpointers.c $(FLAGS) -o mainpointers.o
clean :
rm -f *.o
rm -f prog
I've done some research, none of which has helped me solve this issue.

Answer 1

You're very likely finding that the compiler is optimizing away your code, because the functions have no side-effects. (If you're not familiar with the concept of side effects, the gist is 'changes to program state that might influence other parts of the program'---compilers aggressively prune away side-effect-free code because, by definition, doing so doesn't change the behavior of the program.)
Even allocating memory isn't a side affect, because correct code should never be able to tell whether another part of the program has allocated memory.
The easiest side-effect is to print out the result of any intermediate computation you want to inspect via the debugger; that will force the optimizer to leave the code in place.
E.g.,
int foo() //no side effects, will be optimized to an empty function or pruned.
{
char *test = malloc(4096);
strcpy(test, "My test string");
return 0;
}
int foo() //dumb side effects
{
char *test = malloc(4096);
strcpy(test, "My test string");
printf("%02x", ((int)test & 0xff) ^ (test[0]) );//make output depend on the operations you wish to observe
return 0;
}
An alternate means to verify that the compiler is pruning away your code would be to disassemble the resulting object file...you should see that the functions consist of a single 'return' instruction...which is what the debugger is showing by highlighting the closing curly brace.