The following code is generating a stack overflow error for me
int main(int argc, char* argv[])
{
int sieve[2000000];
return 0;
}
How do I get around this? I am using Turbo C++ but would like to keep my code in C
EDIT:
Thanks for the advice. The code above was only for example, I actually declare the array in a function and not in sub main. Also, I needed the array to be initialized to zeros, so when I googled malloc, I discovered that calloc was perfect for my purposes.
Malloc/calloc also has the advantage over allocating on the stack of allowing me to declare the size using a variable.
Your array is way too big to fit into the stack, consider using the heap:
int *sieve = malloc(2000000 * sizeof(*sieve));
If you really want to change the stack size, take a look at this document.
Tip: - Don't forget to free your dynamically allocated memory when it's no-longer needed.
There are 3 ways:
Allocate array on heap - use malloc(), as other posters suggested. Do not forget to free() it (although for main() it is not that important - OS will clean up memory for you on program termination).
Declare the array on unit level - it will be allocated in data segment and visible for everybody (adding static to declaration will limit the visibility to unit).
Declare your array as static - in this case it will be allocated in data segment, but visible only in main().
That's about 7MB of stack space. In visual studio you would use /STACK:###,### to reflect the size you want. If you truely want a huge stack (could be a good reason, using LISP or something :), even the heap is limited to small'sh allocations before forcing you to use VirtualAlloc), you may also want to set your PE to build with /LARGEADDRESSAAWARE (Visual Studio's linker again), but this configure's your PE header to allow your compiled binary to address the full 4GB of 32'bit address space (if running in a WOW64). If building truely massive binaries, you would also typically need to configure /bigobj as an additional linker paramerter.
And if you still need more space, you can radically violate convention by using something simular to (again MSVC's link) /merge:, which will allow you to pack one section into another, so you can use every single byte for a single shared code/data section. Naturally you would also need to configure the SECTIONS permissions in a def file or with #pgrama.
Use malloc. All check the return type is not null, if it is null then your system simply doesn't have enought memory to fit that many values.
You would be better off allocating it on the heap, not the stack. something like
int main(int argc, char* argv[])
{
int * sieve;
sieve = malloc(20000);
return 0;
}
Your array is huge.
It's possible that your machine or OS don't have or want to allocate so much memory.
If you absolutely need an enormous array, you can try to allocate it dynamically (using malloc(...)), but then you're at risk of leaking memory. Don't forget to free the memory.
The advantage of malloc is that it tries to allocate memory on the heap instead of the stack (therefore you won't get a stack overflow).
You can check the value that malloc returns to see if the allocation succeeded or failed.
If it fails, just try to malloc a smaller array.
Another option would be to use a different data structure that can be resized on the fly (like a linked list). Wether this option is good depends on what you are going to do with the data.
Yet another option would be to store things in a file, streaming data on the fly. This approach is the slowest.
If you go for storage on the hard drive, you might as well use an existing library (for databases)
As Turbo C/C++ is 16 bit compiler int datatype consumes about 2 bytes.
2bytes*2000000=40,00,000 bytes=3.8147MB space.
The auto variables of a function is stored in stack and it caused the overflow of the stack memory. Instead use the data memory [using static or global variable] or the dynamic heap memory [using the malloc/calloc] for creating the required memory as per the availability of the processor memory mapping.
Is there some reason why you can't use alloca() to allocate the space you need on the stack frame based on how big the object really needs to be?
If you do that, and still bust the stack, put it in allocated heap. I highly recommend NOT declaring it as static in main() and putting it in the data segment.
If it really has to be that big and your program can't allocate it on the heap, your program really has no business running on that type of machine to begin with.
What (exactly) are you trying to accomplish?
Related
I am using Dev C++ to write a simulation program. For it, I need to declare a single dimensional array with the data type double. It contains 4200000 elements - like double n[4200000].
The compiler shows no error, but the program exits on execution. I have checked, and the program executes just fine for an array having 5000 elements.
Now, I know that declaring such a large array on the stack is not recommended. However, the thing is that the simulation requires me to call specific elements from the array multiple times - for example, I might need the value of n[234] or n[46664] for a given calculation. Therefore, I need an array in which it is easier to sift through elements.
Is there a way I can declare this array on the stack?
No there is no(we'll say "reasonable") way to declare this array on the stack. You can however declare the pointer on the stack, and set aside a bit of memory on the heap.
double *n = new double[4200000];
accessing n[234] of this, should be no quicker than accessing n[234] of an array that you declared like this:
double n[500];
Or even better, you could use vectors
std::vector<int> someElements(4200000);
someElements[234];//Is equally fast as our n[234] from other examples, if you optimize (-O3) and the difference on small programs is negligible if you don't(+5%)
Which if you optimize with -O3, is just as fast as an array, and much safer. As with the
double *n = new double[4200000];
solution you will leak memory unless you do this:
delete[] n;
And with exceptions and various things, this is a very unsafe way of doing things.
You can increase your stack size. Try adding these options to your link flags:
-Wl,--stack,36000000
It might be too large though (I'm not sure if Windows places an upper limit on stack size.) In reality though, you shouldn't do that even if it works. Use dynamic memory allocation, as pointed out in the other answers.
(Weird, writing an answer and hoping it won't get accepted... :-P)
Yes, you can declare this array on the stack (with a little extra work), but it is not wise.
There is no justifiable reason why the array has to live on the stack.
The overhead of dynamically allocating a single array once is neglegible (you could say "zero"), and a smart pointer will safely take care of not leaking memory, if that is your concern.
Stack allocated memory is not in any way different from heap allocated memory (apart from some caching effects for small objects, but these do not apply here).
Insofar, just don't do it.
If you insist that you must allocate the array on the stack, you will need to reserve 32 megabytes of stack space first (preferrably a bit more). For that, using Dev-C++ (which presumes Windows+MingW) you will either need to set the reserved stack size for your executable using compiler flags such as -Wl,--stack,34000000 (this reserves somewhat more than 32MiB), or create a thread (which lets you specify a reserved stack size for that thread).
But really, again, just don't do that. There's nothing wrong with allocating a huge array dynamically.
Are there any reasons you want this on the stack specifically?
I'm asking because the following will give you a construct that can be used in a similar way (especially accessing values using array[index]), but it is a lot less limited in size (total max size depending on 32bit/64bit memory model and available memory (RAM and swap memory)) because it is allocated from the heap.
int arraysize= 4200000;
int *heaparray= new int[arraysize];
...
k= heaparray[456];
...
delete [] heaparray;
return;
The following code is generating a stack overflow error for me
int main(int argc, char* argv[])
{
int sieve[2000000];
return 0;
}
How do I get around this? I am using Turbo C++ but would like to keep my code in C
EDIT:
Thanks for the advice. The code above was only for example, I actually declare the array in a function and not in sub main. Also, I needed the array to be initialized to zeros, so when I googled malloc, I discovered that calloc was perfect for my purposes.
Malloc/calloc also has the advantage over allocating on the stack of allowing me to declare the size using a variable.
Your array is way too big to fit into the stack, consider using the heap:
int *sieve = malloc(2000000 * sizeof(*sieve));
If you really want to change the stack size, take a look at this document.
Tip: - Don't forget to free your dynamically allocated memory when it's no-longer needed.
There are 3 ways:
Allocate array on heap - use malloc(), as other posters suggested. Do not forget to free() it (although for main() it is not that important - OS will clean up memory for you on program termination).
Declare the array on unit level - it will be allocated in data segment and visible for everybody (adding static to declaration will limit the visibility to unit).
Declare your array as static - in this case it will be allocated in data segment, but visible only in main().
That's about 7MB of stack space. In visual studio you would use /STACK:###,### to reflect the size you want. If you truely want a huge stack (could be a good reason, using LISP or something :), even the heap is limited to small'sh allocations before forcing you to use VirtualAlloc), you may also want to set your PE to build with /LARGEADDRESSAAWARE (Visual Studio's linker again), but this configure's your PE header to allow your compiled binary to address the full 4GB of 32'bit address space (if running in a WOW64). If building truely massive binaries, you would also typically need to configure /bigobj as an additional linker paramerter.
And if you still need more space, you can radically violate convention by using something simular to (again MSVC's link) /merge:, which will allow you to pack one section into another, so you can use every single byte for a single shared code/data section. Naturally you would also need to configure the SECTIONS permissions in a def file or with #pgrama.
Use malloc. All check the return type is not null, if it is null then your system simply doesn't have enought memory to fit that many values.
You would be better off allocating it on the heap, not the stack. something like
int main(int argc, char* argv[])
{
int * sieve;
sieve = malloc(20000);
return 0;
}
Your array is huge.
It's possible that your machine or OS don't have or want to allocate so much memory.
If you absolutely need an enormous array, you can try to allocate it dynamically (using malloc(...)), but then you're at risk of leaking memory. Don't forget to free the memory.
The advantage of malloc is that it tries to allocate memory on the heap instead of the stack (therefore you won't get a stack overflow).
You can check the value that malloc returns to see if the allocation succeeded or failed.
If it fails, just try to malloc a smaller array.
Another option would be to use a different data structure that can be resized on the fly (like a linked list). Wether this option is good depends on what you are going to do with the data.
Yet another option would be to store things in a file, streaming data on the fly. This approach is the slowest.
If you go for storage on the hard drive, you might as well use an existing library (for databases)
As Turbo C/C++ is 16 bit compiler int datatype consumes about 2 bytes.
2bytes*2000000=40,00,000 bytes=3.8147MB space.
The auto variables of a function is stored in stack and it caused the overflow of the stack memory. Instead use the data memory [using static or global variable] or the dynamic heap memory [using the malloc/calloc] for creating the required memory as per the availability of the processor memory mapping.
Is there some reason why you can't use alloca() to allocate the space you need on the stack frame based on how big the object really needs to be?
If you do that, and still bust the stack, put it in allocated heap. I highly recommend NOT declaring it as static in main() and putting it in the data segment.
If it really has to be that big and your program can't allocate it on the heap, your program really has no business running on that type of machine to begin with.
What (exactly) are you trying to accomplish?
The following code is generating a stack overflow error for me
int main(int argc, char* argv[])
{
int sieve[2000000];
return 0;
}
How do I get around this? I am using Turbo C++ but would like to keep my code in C
EDIT:
Thanks for the advice. The code above was only for example, I actually declare the array in a function and not in sub main. Also, I needed the array to be initialized to zeros, so when I googled malloc, I discovered that calloc was perfect for my purposes.
Malloc/calloc also has the advantage over allocating on the stack of allowing me to declare the size using a variable.
Your array is way too big to fit into the stack, consider using the heap:
int *sieve = malloc(2000000 * sizeof(*sieve));
If you really want to change the stack size, take a look at this document.
Tip: - Don't forget to free your dynamically allocated memory when it's no-longer needed.
There are 3 ways:
Allocate array on heap - use malloc(), as other posters suggested. Do not forget to free() it (although for main() it is not that important - OS will clean up memory for you on program termination).
Declare the array on unit level - it will be allocated in data segment and visible for everybody (adding static to declaration will limit the visibility to unit).
Declare your array as static - in this case it will be allocated in data segment, but visible only in main().
That's about 7MB of stack space. In visual studio you would use /STACK:###,### to reflect the size you want. If you truely want a huge stack (could be a good reason, using LISP or something :), even the heap is limited to small'sh allocations before forcing you to use VirtualAlloc), you may also want to set your PE to build with /LARGEADDRESSAAWARE (Visual Studio's linker again), but this configure's your PE header to allow your compiled binary to address the full 4GB of 32'bit address space (if running in a WOW64). If building truely massive binaries, you would also typically need to configure /bigobj as an additional linker paramerter.
And if you still need more space, you can radically violate convention by using something simular to (again MSVC's link) /merge:, which will allow you to pack one section into another, so you can use every single byte for a single shared code/data section. Naturally you would also need to configure the SECTIONS permissions in a def file or with #pgrama.
Use malloc. All check the return type is not null, if it is null then your system simply doesn't have enought memory to fit that many values.
You would be better off allocating it on the heap, not the stack. something like
int main(int argc, char* argv[])
{
int * sieve;
sieve = malloc(20000);
return 0;
}
Your array is huge.
It's possible that your machine or OS don't have or want to allocate so much memory.
If you absolutely need an enormous array, you can try to allocate it dynamically (using malloc(...)), but then you're at risk of leaking memory. Don't forget to free the memory.
The advantage of malloc is that it tries to allocate memory on the heap instead of the stack (therefore you won't get a stack overflow).
You can check the value that malloc returns to see if the allocation succeeded or failed.
If it fails, just try to malloc a smaller array.
Another option would be to use a different data structure that can be resized on the fly (like a linked list). Wether this option is good depends on what you are going to do with the data.
Yet another option would be to store things in a file, streaming data on the fly. This approach is the slowest.
If you go for storage on the hard drive, you might as well use an existing library (for databases)
As Turbo C/C++ is 16 bit compiler int datatype consumes about 2 bytes.
2bytes*2000000=40,00,000 bytes=3.8147MB space.
The auto variables of a function is stored in stack and it caused the overflow of the stack memory. Instead use the data memory [using static or global variable] or the dynamic heap memory [using the malloc/calloc] for creating the required memory as per the availability of the processor memory mapping.
Is there some reason why you can't use alloca() to allocate the space you need on the stack frame based on how big the object really needs to be?
If you do that, and still bust the stack, put it in allocated heap. I highly recommend NOT declaring it as static in main() and putting it in the data segment.
If it really has to be that big and your program can't allocate it on the heap, your program really has no business running on that type of machine to begin with.
What (exactly) are you trying to accomplish?
I try to create a ~975KB array on the stack and it crashes.
const int size = 500;
cout << (sizeof(float)*size*size)/1024 << endl;
float myArray[size*size]; // crash
This seems like a very small amount of space. Is there any way to know how much space is available (total and currently) before I initialize a variable?
The stack is limited in nearly all systems. How big it's allowed to be depends on the OS/Compiler combination. Putting VERY large amounts of data on the stack is a poor idea. Either use C++ standard types (e.g. vector) or use your own dynamic memory allocation. You never know when some other function adds a bit of extra stack, and all of a sudden, you go over the limit - best to not get anywhere near the max size of the stack.
In Visual C++ the default stack size is managed by the linker option /STACK (doc). By default it is 1 MB.
Note that each new thread will have its own stack, and you can specify the initial size with parameter dwStackSize in function CreateThread. If it is 0 it will default to the one used in the linker command.
About your other questions, there is no way to query the current/maximum stack size. To avoid problems it is better to use the heap for any significant memory allocation.
The default stack size for Visual Studio is 1MB, as Andre said you can use std::vector to avoid this problem or you can dynamically allocate memory. You can adjust the stack size on Visual Studio using /F. If there is not a compelling reason to allocate the data on the stack it probably makes more sense to use another option.
When writing C++ code I've learned that using the stack to store memory is a good idea.
But recently I ran into a problem:
I had an experiment that had code that looked like this:
void fun(const unsigned int N) {
float data_1[N*N];
float data_2[N*N];
/* Do magic */
}
The code exploted with a seqmentation fault at random, and I had no idea why.
It turned out that problem was that I was trying to store things that were to big on my stack, is there a way of detecting this? Or at least detecting that it has gone wrong?
float data_1[N*N];
float data_2[N*N];
These are variable length arrays (VLA), as N is not a constant expression. The const-ness in the parameter only ensures that N is read-only. It doesn't tell the compiler that N is constant expression.
VLAs are allowed in C99 only; in other version of C, and all versions of C++ they're not allowed. However, some compilers provides VLA as compiler-extension feature. If you're compiling with GCC, then try using -pedantic option, it will tell you it is not allowed.
Now why your program gives segfault, probably because of stack-overflow due to large value of N * N:
Consider using std::vector as:
#include <vector>
void fun(const unsigned int N)
{
std::vector<float> data_1(N*N);
std::vector<float> data_2(N*N);
//your code
}
It's extremely difficult to detect that the stack is full, and not at all portable. One of the biggest problems is that stack frames are of variable size (especially when using variable-length arrays, which are really just a more standard way of doing what people were doing before with alloca()) so you can't use simple proxies like the number of stack frames.
One of the simplest methods that is mostly portable is to put a variable (probably of type char so that a pointer to it is a char*) at a known depth on the stack and to then measure the distance from that point to a variable (of the same type) in the current stack frame by simple pointer arithmetic. Add in an estimate of how much space you're about to allocate, and you can have a good guess as to wether the stack is about to blow up on you. The problems with this are that you don't know the direction that the stack is growing in (no, they don't all grow in the same direction!) and working out the size of the stack space is itself rather messy (you can try things like system limits, but they're really quite awkward). Plus the hack factor is very high.
The other trick I've seen used on 32-bit Windows only was to try to alloca() sufficient space and handle the system exception that would occur if there was insufficient room.
int have_enough_stack_space(void) {
int enough_space = 0;
__try { /* Yes, that's got a double-underscore. */
alloca(SOME_VALUE_THAT_MEANS_ENOUGH_SPACE);
enough_space = 1;
} __except (EXCEPTION_EXECUTE_HANDLER) {}
return enough_space;
}
This code is very non-portable (e.g., don't count on it working on 64-bit Windows) and building with older gcc requires some nasty inline assembler instead! Structured exception handling (which this is a use of) is amongst the blackest of black arts on Windows. (And don't return from inside the __try construct.)
Try using instead functions like malloc. It will return null explicitly, if it failed to find a block of memory of the size you requested.
Of course, in that case don't forget to free this memory in the end of function, after you are done.
Also, you can check the settings of your compiler, with what stack memory limit it generates the binaries.
One of the reasons people say it is better to use stack instead of heap memory can be because of the fact that variables allocated on top of the stack will be popped out automatically when you leave the body of the function. For storing big blocks of information it is usual to use heap memory and other data structures like linked lists or trees. Also memories allocated on the stack is limited and much more less than you can allocate in the heap space. I think it is better to manage the memory allocation and releasing more carefully instead of trying to use stack for storing big data.
You can use framework which manage your memory allocations. As well you can use VDL to check your memory leaks and memories which is not released.
is there a way of detecting this?
No, in general.
Stack size is platform depedent. Typically, Operating System decides the size of the stack. So you can check your OS (ulimit -s on linux) to see how much stack memory it allocates for your program.
If your compiler supports stackavail() then you can check it. It's better to go heap-allocated memory in situations where you are unsure whether you'd exceed the stack limit.