I have a function in which I dynamically allocate an array and then use it later, but it changes arbitrarily in between uses:
void func(void){
//allocate two arrays. Tried both malloc and calloc
my_obj* array = calloc(arr_length, sizeof(my_obj*));
my_obj2* array2 = calloc(arr_length_2, sizeof(my_obj2*));
//now I fill the first array with some items
for(int i = 0; i < arr_length; i ){
my_obj o = {1, 2, 3, 4};
array[i] = o;
}
//now I test to make sure I filled the array as planned
for(int i = 0; i < arr_length; i ){
printf("%d\n", array[i].x);
}
//everything prints as planned!
//now I fill the second array, without ever touching the first
for(int i = 0; i < arr_length_2; i ){
my_obj2 o = {1, 2};
array2[i] = o;
}
//now I print the first array again. Instead of the contexts I expect,
//it is full of random data, seemingly completely unrelated to either its
//previous contents or the contents of the second array!
for(int i = 0; i < arr_length; i ){
printf("%d\n", array[i].x);
}
}
As mentioned in the comments of the code, it seems like my array is magically changing without me ever touching it. Is there a bug which could cause this? It's worth noting that I am running my code on a VirtualBox VM running Ubuntu. I don't receive any kind of error message. I have triple checked that I really am not touching the first array in between the two print routines.
CodePudding user response:
sizeof(my_obj*)
is pointer size
my_obj* array = calloc(arr_length, sizeof(my_obj*));
my_obj2* array2 = calloc(arr_length_2, sizeof(my_obj2*));
Here your'e trying to access memory that you havent allocated:
...
array[i] = o;