Visual C++ Array Size Crash [duplicate]

Question

Possible Duplicate:
Stack overflow visual C++, potentially array size?

This code is simply meant to read values from a binary file into the array DataBuffer. When the size of DataBuffer is greater than or equal to 515000, it simply crashes. I am developing this in Visual C++ 2010 on Windows 7. The function cbFileRead() is something whose source code I can not access. cbFileRead() expects DataBuffer to be of the type USHORT*.

#include <stdio.h>  // printf()
#include "cbw.h"    // cbFileRead()

int main(int argc, char* argv[]) {

    // Declarations
    char* FileName = argv[1];
    long FirstPoint = 0;
    long NumPoints;

    // Set data collection sizes
    const long chunkSize = 515000;
    NumPoints = chunkSize; // Number of points to be read into mem
    WORD DataBuffer[chunkSize-1];

    // Get data
    cbFileRead(FileName, FirstPoint, &NumPoints, DataBuffer);

    printf("Completed on data point %d whose value is %d\n", NumPoints, DataBuffer[chunkSize-1]);

    return 0;
}

What reasons are there for this crashing? I would expect the array size to be able to go much higher.

You typically have a pretty small stack by default. I'd use std::vector instead — Flexo - Save the data dump
– Flexo - Save the data dump ♦, Commented Jul 11, 2012 at 14:10
@thoughtadvances you almost certainly don't have a multi-gigabyte stack. It's normally only a megabyte or so. — Flexo - Save the data dump
– Flexo - Save the data dump ♦, Commented Jul 11, 2012 at 14:14

hmjd · Accepted Answer · 2012-07-11 14:24:01Z

4

The printf() is going beyond the end of the array DataBuffer, as it has chunksize - 1 elements so the last element is chunksize - 1 - 1. The function cbFileRead() is (possibly) misinformed of the number of elements in DataBuffer also.

EDIT:

As others have already stated, the default stack size is 1MB. The size of the DataBuffer array is 2 * 515000 which equals 1030000, which leaves 18576 free bytes on the stack. cbFileRead() could easily be declaring a large buffer on the stack for reading from file. As suggested by everyone else, allocate the DataBuffer on the heap using new[] (and delete[] to free) or use vector<WORD>.

edited Jul 11, 2012 at 14:24

answered Jul 11, 2012 at 14:12

hmjd

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3 Comments

user7116 Over a year ago

+1, that's a problem too (didn't scroll his code enough!).

Xander Dunn Over a year ago

Thanks. FirstPoint = 0, so I think cbFileRead() is getting the correct numbers. I want chunkSize elements, so they are stored in an array of chunkSize() - 1. Because the array is also null indexed, the last element of the array is then chunkSize()-2. Is that right?

hmjd Over a year ago

@thoughtadvances, but the array was declared as having chunkSize - 1 elements. If it has chunkSize elements then valid indexes are from 0 to chunkSize - 1.

Chris Dargis · Accepted Answer · 2012-07-11 14:19:59Z

2

The default stack reservation size used by the linker is 1 MB. To specify a different default stack reservation size for all threads and fibers, use the STACKSIZE statement in the module definition (.def) file.

Microsoft Dev Center - Thread Stack Size

Or you can allocate the memory dynamically with the new keyword.

edited Jul 11, 2012 at 14:19

answered Jul 11, 2012 at 14:14

Chris Dargis

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1 Comment

Xander Dunn Over a year ago

Thanks. I just discovered that new is capable of doing this.

user7116 · Accepted Answer · 2012-07-11 14:13:00Z

1

Your stack size may not be large enough to handle local data of that size (assuming this is what you mean by "crash"):

// use dynamic allocation instead of stack local
WORD *DataBuffer = new WORD[chunkSize];

cbFileRead(FileName, FirstPoint, &NumPoints, DataBuffer);

// ...use DataBuffer...

// deallocate DataBuffer when done
delete[] DataBuffer;

answered Jul 11, 2012 at 14:13

user7116

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1 Comment

hmjd Over a year ago

+1 returned as this a probable cause.

Mike Seymour · Accepted Answer · 2012-07-11 14:18:41Z

1

On most platforms, including Windows, local variables are stored on a stack, which has a limited size - in this case, it looks like it's around 1MB. There's probably a way to increase that size if you really need to, but it would be better to allocate large arrays dynamically:

#include <vector>

std::vector<WORD> DataBuffer(chunkSize); // guessing that "chunkSize-1" was an error

cbFileRead(FileName, FirstPoint, &NumPoints, &DataBuffer[0]);

printf("Completed on data point %d whose value is %d\n", 
       NumPoints, DataBuffer[chunkSize-1]);

Note that, if the array size is actually supposed to be chunkSize-1, then the last element would be DataBuffer[chunkSize-2], since arrays are indexed from zero.

answered Jul 11, 2012 at 14:18

Mike Seymour

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