C program, "Uninitialized Value Error" on initialized int array - arrays

Question

Update:
Removing the print statement (line 52) entirely with all else the same as in the code below gave me 0 errors. The errors exist within my functions when printing (using philo[i]) and in this print statement (added for debugging), but do not exist if I run the entire program with no prints. Any ideas what I'm doing wrong???
Thank you for the help so far. I have made a couple of changes based on comments received so far.
***** Original (Edited) Question *****
I can't figure out why I have been getting this error, "Uninitialised value was created by a stack allocation". I started with a completed program that works fine, but gives me a ton of uninitialized value errors. I have traced the problem down to a few lines of code by excluding all functions and adding additional print statements. This code is to solve the dining philosopher's problem using threads (homework), so I don't want to post too much. My code is now:
#include <all needed header files>
#define NUM_PHIL 5
#define MIN_EAT_TIME 10
pthread_t philosopher[NUM_PHIL]; // array to hold IDs for philosopher threads
pthread_mutex_t chopstick[NUM_PHIL]; // array to hold IDs for chopstick mutexes (locks)
// function definitions here:
int philosopherFun(int *philo);
// All others have been bypassed at the time of my current problem
int main(int argc, char *argv[]) {
int phil[NUM_PHIL]; // Philosopher numbers ("names")
for(int i = 0; i < NUM_PHIL; i++) {
phil[i] = i + 1;
}
for(int i = 0; i < NUM_PHIL; i++) {
// Print statement causes valgrind error to exist (as does calling a function using phil)
printf("Value phil[%d] = %d\n", i, phil[i]);
}
// Initilize mutexes for chopsticks, report error as needed
for(int i = 0; i < NUM_PHIL; i++) {
if(pthread_mutex_init( stuff here) < 0) {
// error reporting
// print statement uses i
}
}
for(int i = 0; i < NUM_PHIL; i++) {
if(pthread_create(&philosopher[i], NULL, (void*) philosopherFun, (void*) &phil[i] ) != 0) {
// error reporting
// print statement uses phil[i]
}
}
/* Code omitted as this is Homework */
// Join threads created for philosophers (using pthread_join)
// error reporting
// print statement uses phil[i]
// Destroy chopstick mutexes when done. (using pthread_mutex_destroy)
// error reporting
// print statement uses i
printf("The philosophers have all finished eating and its time for bed. Goodnight...\n");
return 0;
}
int philosopherFun(int *philo) {
return 0;
}
Program output:
Value phil[0] = 1
Value phil[1] = 2
Value phil[2] = 3
Value phil[3] = 4
Value phil[4] = 5
The philosophers have all finished eating and its time for bed. Goodnight...
My Valgrind errors are:
==46556== HEAP SUMMARY:
==46556== in use at exit: 0 bytes in 0 blocks
==46556== total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==46556==
==46556== All heap blocks were freed -- no leaks are possible
==46556==
==46556== ERROR SUMMARY: 10 errors from 1 contexts (suppressed: 0 from 0)
==46556==
==46556== 10 errors in context 1 of 1:
==46556== Conditional jump or move depends on uninitialised value(s)
==46556== at 0x7FFF205A395F: ??? (in /dev/ttys000)
==46556== by 0x7FFF2046FFFA: ??? (in /dev/ttys000)
==46556== by 0x7FFF20478CF0: ??? (in /dev/ttys000)
==46556== by 0x7FFF2049D8B8: ??? (in /dev/ttys000)
==46556== by 0x7FFF20475EF5: ??? (in /dev/ttys000)
==46556== by 0x7FFF20474061: ??? (in /dev/ttys000)
==46556== by 0x1000038CD: main (philo.c:52)
==46556== Uninitialised value was created by a stack allocation
==46556== at 0x7FFF20475FDF: ??? (in /dev/ttys000)
==46556==
==46556== ERROR SUMMARY: 10 errors from 1 contexts (suppressed: 0 from 0)
line 52 is my print statement:
printf("Value phil[%d] = %d\n", i, phil[i]);
which I believe accounts for 5 errors (phil[0] - phil[4]) and I call philosopherFun in my pthread_create on line 68 (this line of code included), again accounting for 5 errors (1 for each thread). This function is currently only returning on the first line, so none of the rest of my program is involved (though I started with 50-250 errors depending on my parameters and which functions I excluded).
I feel like my int array (int phil[]) is causing the problem, but it is immediately initialized, so I'm not sure how this is happening. Please help!
Thanks,
Kristine
Edited... Added some comments from omitted code- Threads are joined and mutexes destroyed
I also tried making int phil[NUM_PHIL] global by declaring it outside of my main function, but this made no change to the errors returned by Valgrind. defining phil[5] = {1, 2, 3, 4, 5}; as a global also didn't help.

Answer 1

I believe this is where your problem comes from:
int phil[NUM_PHIL];
and here
if(pthread_create(&philosopher[i], NULL, (void*) philosopherFun, (void*) &phil[i] ) != 0) {
more code ...
}
You're referencing a stack-allocated object (you're getting a pointer to the elements of the philo array). When the main function returns, the memory will be deleted and the other threads will still be holding on to garbage. To be sure this is the problem, move your philo array to a global scope, or allocate the array on the heap instead.