Question

A part of my code will read in an unknown number of lines from a text file, parse that line into a structure (tempSomeStruct), resize the SomeStruct_Array, and then add that tempSomeStruct into the newly opened spot in memory.

However after a few times through the while loop, my program stops and says

myApplication.exe has triggered a breakpoint.

I did not set a breakpoint, and doing some digging, it LOOKS like the breakpoint is due to heap corruption from my call to realloc. I am pretty new to dynamic allocation, so while I have searched and found a few possible causes, so far no fixes have worked.

How am I corrupting the heap in this situation, and what do I do differently to avoid doing so?

I have a function like this:

int growArray(SomeStruct **SomeStruct_Array,int currentSize, int numNewElements)
{
    const int totalSize = currentSize + numNewElements;
    SomeStruct *temp = (SomeStruct*)realloc(*SomeStruct_Array,(totalSize * sizeof(SomeStruct)));
    if (temp == NULL)
    {
        printf("Cannot allocate more memory.\n");
        return 0;
    }
    else
    {
        *SomeStruct_Array = temp;
    }

    return totalSize;
}

and it is called in elsewhere like this:

SomeStruct* SomeStruct_Array = (SomeStruct *) calloc(1,sizeof(SomeStruct));
int Error_Array_Size = 0;

if(SomeStruct_Array == NULL)
{
   printf("Cannot allocate initial memory for data\n");
   return;
}

while(fgets(line,sizeof(line), file) != NULL)
{
   parseTextIntoSomeStruct(line, &tempSomeStruct);
   SomeStruct_Array_Size = growArray(&SomeStruct_Array,SomeStruct_Array_Size,1);
   if(SomeStruct_Array_Size > 0)
   {
      SomeStruct_Array[SomeStruct_Array_Size] = tempSomeStruct;
   }
}

Answer 1

Your new array’s size is SomeStruct_Array_Size, and you immediately write to SomeStruct_Array[SomeStruct_Array_Size] which is one past the end of the array! Remember, C arrays are zero-indexed.

Use

SomeStruct_Array[SomeStruct_Array_Size-1] = tempSomeStruct;

instead.