QVector crashes when array size is big

[wysota]

Just wrote and tested my own linked list, it works fine.

Which proves exactly nothing.

[Sheng]

Which proves exactly nothing.

It at least demonstrated the problem is not from the limitation of the system, but from the container.

[drhex]

I've experimented some more and abbreviated the program:

#include<QVector>
 
struct myStruc {
    int array[3000*2000];
};
 
int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);
 
    QVector<myStruc> myVector;
    myStruc currentStruc;
    myVector.push_back(currentStruc);
}

#include<QVector>

struct myStruc {
    int array[3000*2000];
};

int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);

    QVector<myStruc> myVector;
    myStruc currentStruc;
    myVector.push_back(currentStruc);
}

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For array-sizes upto 3000*232 (=2.8MB), the above program works as expected.

For array-sizes between 3000*233 and 3000*698, it prints "hello" and then segfaults.

For array-sizes 3000*699 (=8.4MB) and up, it segfaults immediately, without even printing "hello".

Adding a QApplication object did not help.

Tested with gcc 4.3.2 on Ubuntu 8.10 using Qt-4.5.0-beta1.

Sheng, you've found the struct-of-death!

[Sheng]

I've experimented some more and abbreviated the program:

#include<QVector>
 
struct myStruc {
    int array[3000*2000];
};
 
int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);
 
    QVector<myStruc> myVector;
    myStruc currentStruc;
    myVector.push_back(currentStruc);
}

#include<QVector>

struct myStruc {
    int array[3000*2000];
};

int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);

    QVector<myStruc> myVector;
    myStruc currentStruc;
    myVector.push_back(currentStruc);
}

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For array-sizes upto 3000*232 (=2.8MB), the above program works as expected.

For array-sizes between 3000*233 and 3000*698, it prints "hello" and then segfaults.

For array-sizes 3000*699 (=8.4MB) and up, it segfaults immediately, without even printing "hello".

Adding a QApplication object did not help.

Tested with gcc 4.3.2 on Ubuntu 8.10 using Qt-4.5.0-beta1.

Sheng, you've found the struct-of-death!

Nice research, thanks.

[drhex]

#include <stdio.h>
#include <unistd.h>
 
struct myStruc {
    int array[3000*2000];
};
 
 
void foo(const myStruc &v)
{
    printf("%d\n", v.array[1]);
}
 
int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);
 
    myStruc currentStruc;
    foo(currentStruc);
}

#include <stdio.h>
#include <unistd.h>

struct myStruc {
    int array[3000*2000];
};


void foo(const myStruc &v)
{
    printf("%d\n", v.array[1]);
}

int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);

    myStruc currentStruc;
    foo(currentStruc);
}

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The above also crashes without printing hello, and now there isn't any Qt code left! Seems like a compiler or OS problem.

[Sheng]

#include <stdio.h>
#include <unistd.h>
 
struct myStruc {
    int array[3000*2000];
};
 
 
void foo(const myStruc &v)
{
    printf("%d\n", v.array[1]);
}
 
int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);
 
    myStruc currentStruc;
    foo(currentStruc);
}

#include <stdio.h>
#include <unistd.h>

struct myStruc {
    int array[3000*2000];
};


void foo(const myStruc &v)
{
    printf("%d\n", v.array[1]);
}

int main(int , char* [])
{
    printf("hello\n");
    fflush(stdout);
    sleep(1);

    myStruc currentStruc;
    foo(currentStruc);
}

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The above also crashes without printing hello, and now there isn't any Qt code left! Seems like a compiler or OS problem.

try use heap to see what happens. Should work fine, then try to push back to the container.
Here is what I got:
hello
0
segmentation fault

[drhex]

#include <stdio.h>
#include <sys/resource.h>
 
int main(int , char *[])
{
    struct rlimit rlim;
    getrlimit(RLIMIT_STACK, &rlim);
    printf("max stack size=%d bytes\n", (int)rlim.rlim_cur);
}

#include <stdio.h>
#include <sys/resource.h>

int main(int , char *[])
{
    struct rlimit rlim;
    getrlimit(RLIMIT_STACK, &rlim);
    printf("max stack size=%d bytes\n", (int)rlim.rlim_cur);
}

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This prints

max stack size=8388608 bytes

on my machine. One learns something every day!

[drhex]

try use heap to see what happens. Should work fine, then try to push back to the container.
Here is what I got:
hello
0
segmentation fault

Try using a pointer or a QVector in myStruc instead of that huge int array.

[wysota]

Or a type shorter than int.

[Sheng]

Or a type shorter than int.

Yes, actually I used uint8_t in my code.

Try using a pointer or a QVector in myStruc instead of that huge int array.

I can not use pointer since I need to save image data in the queue.