Why doesnt this C Code Work

[digitalzero]

#include <stdio.h>

struct Person
{
int age;
};

struct Person *getAge();

int main()
{
struct Person *p;
p = getAge();
printf("Age: %d\n",(*p).age);
return 0;
}

struct Person *getAge()
{
struct Person *result;

(*result).age = 10;

return result;
}


It compiles fine but when your run it: Age is -1929102879 or something

[goon12]

hrm.. Not too sure but you could try:


printf("Age: %d\n", p->age);

instead of

printf("Age: %d\n",(*p).age);

[digitalzero]

Still the same problem... after changing that

[Energon]

You have to allocate memory for your pointer in getAge(). try:


struct Person* getAge()
{
struct Person* result = (struct Person*)malloc(sizeof(struct Person));

result->age = 10;
return result;
}


Also note the use of the ->, which derefernces the pointer so you don't need the (*result) to dereference.

[bwkaz]

And then remember to:

free(p);

in main() after you print the stuff out.

Actually, I'm surprised it didn't segfault on you...

[TheLinuxDuck]

Originally posted by bwkaz:
<STRONG>Actually, I'm surprised it didn't segfault on you...</STRONG>

It prolly didn't segfault because it's only overwriting 4 bytes. Sometimes it will let us get away with that, if it's a tiny amount. That, of course, also depends on where the pointer points to... (^=

[bwkaz]

Yeah, I suppose. It would definitely have segfaulted if the pointer was initialized to NULL, but if the random value in memory happened to be valid in the process' address space, then I guess it'd be valid.