This question already has answers here:
Stack overflow visual C++, potentially array size?
(2 answers)
Closed 9 years ago.
Why is this code giving segmentation fault? I am using code::blocks.
#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
int a[555555];
}
This is what called stack overflow.
Generally stack size are small and you can't allocate memory in such a large amount on stack.
For this purpose programmers allocate it on heap (using dynamic allocation). In C, you can use malloc family function
int *a = malloc(sizeof(int)*55555); // Use free(a) to deallocate
In C++ you can use new operator
int *b = new int[555555]; // Use delete [] to deallocate
Because you are trying to allocate a bit over 2MB (Previously I failed at math and thought it was 2GB) of memory on stack, which then blows the stack.
Note: for windows the default stack size for a particular thread is 1MB and on Gnu/linux you can find out stack size value using ulimit -s command.
You've come to the right place to ask the question. ;)
The array is large and lives on the stack. The code crashes because it runs out of the limited stack space.
If you allocate a on the heap, the problem will likely disappear.
As other already had told you you are trying to allocate a large amount of memory in the stack which space is usually very limited.
See for instance:
#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
int a[555555];
int* b = new int[555555];
delete [] b;
}
In that snipped, you have two arrays of integers, one allocated in the heap and the other allocated on the stack.
Here you can find some explanations about which are the differences between the heap and the stack:
What and where are the stack and heap?
http://gribblelab.org/CBootcamp/7_Memory_Stack_vs_Heap.html
I've got some considerations on your code.
First, modern compilers will recognize that a is unused and then it'll be thrown away.
But if you put a certain value into a certain position, a will be allocated, even though it's bigger than the stack size. The kernel will not allow you do that: that's why you get a SIGSEGV.
Finally, you should rely on either std::array or std::vector rather than pure C arrays.
Related
This question already has answers here:
Segmentation fault on large array sizes
(7 answers)
Closed 3 years ago.
Program with large global array:
int ar[2000000];
int main()
{
}
Program with large local array:
int main()
{
int ar[2000000];
}
When I declare an array with large size in the main function, the program crashes with "SIGSEGV (Segmentation fault)".
However, when I declare it as global, everything works fine. Why is that?
Declaring the array globally causes the compiler to include the space for the array in the data section of the compiled binary. In this case you have increased the binary size by 8 MB (2000000 * 4 bytes per int). However, this does mean that the memory is available at all times and does not need to be allocated on the stack or heap.
EDIT: #Blue Moon rightly points out that an uninitialized array will most likely be allocated in the bss data segment and may, in fact, take up no additional disk space. An initialized array will be allocated statically.
When you declare an array that large in your program you have probably exceeded the stack size of the program (and ironically caused a stack overflow).
A better way to allocate a large array dynamically is to use a pointer and allocate the memory on the heap like this:
using namespace std;
int main() {
int *ar;
ar = malloc(2000000 * sizeof(int));
if (ar != null) {
// Do something
free(ar);
}
return 0;
}
A good tutorial on the Memory Layout of C Programs can be found here.
This question already has answers here:
Segmentation fault on large array sizes
(7 answers)
Closed 3 years ago.
Program with large global array:
int ar[2000000];
int main()
{
}
Program with large local array:
int main()
{
int ar[2000000];
}
When I declare an array with large size in the main function, the program crashes with "SIGSEGV (Segmentation fault)".
However, when I declare it as global, everything works fine. Why is that?
Declaring the array globally causes the compiler to include the space for the array in the data section of the compiled binary. In this case you have increased the binary size by 8 MB (2000000 * 4 bytes per int). However, this does mean that the memory is available at all times and does not need to be allocated on the stack or heap.
EDIT: #Blue Moon rightly points out that an uninitialized array will most likely be allocated in the bss data segment and may, in fact, take up no additional disk space. An initialized array will be allocated statically.
When you declare an array that large in your program you have probably exceeded the stack size of the program (and ironically caused a stack overflow).
A better way to allocate a large array dynamically is to use a pointer and allocate the memory on the heap like this:
using namespace std;
int main() {
int *ar;
ar = malloc(2000000 * sizeof(int));
if (ar != null) {
// Do something
free(ar);
}
return 0;
}
A good tutorial on the Memory Layout of C Programs can be found here.
This question already has answers here:
Segmentation fault on large array sizes
(7 answers)
Closed 3 years ago.
Program with large global array:
int ar[2000000];
int main()
{
}
Program with large local array:
int main()
{
int ar[2000000];
}
When I declare an array with large size in the main function, the program crashes with "SIGSEGV (Segmentation fault)".
However, when I declare it as global, everything works fine. Why is that?
Declaring the array globally causes the compiler to include the space for the array in the data section of the compiled binary. In this case you have increased the binary size by 8 MB (2000000 * 4 bytes per int). However, this does mean that the memory is available at all times and does not need to be allocated on the stack or heap.
EDIT: #Blue Moon rightly points out that an uninitialized array will most likely be allocated in the bss data segment and may, in fact, take up no additional disk space. An initialized array will be allocated statically.
When you declare an array that large in your program you have probably exceeded the stack size of the program (and ironically caused a stack overflow).
A better way to allocate a large array dynamically is to use a pointer and allocate the memory on the heap like this:
using namespace std;
int main() {
int *ar;
ar = malloc(2000000 * sizeof(int));
if (ar != null) {
// Do something
free(ar);
}
return 0;
}
A good tutorial on the Memory Layout of C Programs can be found here.
This question already has an answer here:
Why does a large local array crash my program, but a global one doesn't? [duplicate]
(1 answer)
Closed 4 years ago.
When I write the following program, it works correctly i.e. the bitset array is declared outside the main() method.
Correctly Works
#include <iostream>
#include <bitset>
using namespace std;
bitset<5000> set[5000];
int main(){
cout<<"program runs fine"<<endl;
return 0;
}
But I get stack-overflow exception when I create it inside the main method. Can anyone explain in detail as to what is going on here? Normally I see stack-overflow exceptions in recursive methods. So who is using the stack here?
#include <iostream>
#include <bitset>
using namespace std;
int main(){
bitset<5000> set[5000];
cout<<"program runs fine"<<endl;
return 0;
}
Doesn't work and throws stack-overflow exception
Declaring it in main is declaring it in "automatic storage" AKA the stack. Declaring it outside of main, is declaring it in "static storage" AKA global data. You are declaring a ton of data. std::bitset<5000> is 632 bytes on my system with VS2013 (likely an alignment from 5000/8). And you are declaring 5000 of them. 5000 * 632 = 3 160 000 bytes, or roughly 3 Megabytes. Default in VS2013 is 1 megabyte for the stack, which is why you are seeing an overflow.
There are three kinds of storage: automatic, storage, and dynamic. These are colloquially referred to as stack, static (in some cases, global) and heap memory respectively:
int static_int;
int main() {
int automatic_int;
static int local_static_int; // also static storage!
int * dynamic_int_ptr = new int;
}
Automatic storage is allocated at a mix of compile time/run time. The stack expands at run-time entry to a function in order to hold local variables, but this is a known compile-time value since the number of variables and their sizes are well known (I'm ignoring dynamic arrays here because they are non-standard) These variables are constructed on scope entry, and destructed on scope exit.
Static storage is allocated at compile time. This memory is paid for up front, and constructed at program start. It is destructed when the program exits.
Dynamic storage is allocated at run-time. This memory is allocated by new and a pointer to some blob that holds your shiny new data is returned. These variables are constructed when new is called, and destructed when delete is called.
Because when you declare array as global, memory is allocated in the data segment of the process while when you try to declare it inside a function, memory is allocated on the stack. Since you are allocating large amount of memory, it results in stackoverflow exception.
Edit: Here is good explanation of the memory allocation.
You are trying to create (5000*5000)/8 bytes - 3Megs of data on the program stack which is causing a Stack Overflow as reported. You do not have enough stack space in your program for this. When you create it as a global, it is inserted in your programs data segment.
This question already has answers here:
Segmentation fault on large array sizes
(7 answers)
Closed 4 years ago.
I'm converting a program from fortran to C++.
My code seems to run fine until I add this array declaration:
float TC[100][100][100];
And then when I run it I get a segmentation fault error. This array should only take up 8Mb of memory and my machine has 3 Gb. Is there a problem with this declaration? My c++ is pretty rusty.
That array is about 4 megabyte large. If this definition is inside a function (as local variable), then the compiler tries to store it on the stack, which on most systems cannot grow that large.
The Fortran compiler probably allocated it statically (Fortran routines are not allowed to be called recursively unless explicitly marked as recursive, so static allocation for local variables works there for non-recursive functions), and therefore the error doesn't occur there.
A simple fix would be to explicitly declare the variable static, assuming the Fortran function was not declared recursive. However this may bite you later, if you ever try to call that function recursively from a revised version. So a better solution would probably be to allocate it dynamically. However that costs extra time and therefore depending on the nature of the code, may hurt your performance too much (Fortran code quite often is numerical code where performance matters).
If you choose to make the array static, you can build in a protection against accidental recursive calls:
void yourfunction()
{
static bool active;
static float TC[100][100][100];
assert(!active);
active = true;
// your code
active = false;
}
I'm guessing TC is being allocated as an auto local variable. This means it's being stored on the stack. You don't get 4mb of stack memory, so it's causing a stack overflow.
To solve it, use dynamic allocation with a structured container or new.
This looks like a stack-based declaration. Try allocating from the heap (i.e. using the new operator).
If you are declaring it inside of a function, as a local variable, it may be that you stack is not big enough to fit the array. You may try to allocate in the heap, with new or malloc(), or, if your design allows, make it a global variable.
In C++ the stack has a limited amount of space. MSVC defaults this size to 1MB. If the stack uses more than 1MB it will segfault or stackoverflow or something. You will have to move that structure to dynamic memory. To move it to dynamic memory, you want something like this:
typedef float (bigarray)[100][100][100];
bigarray& TC() {
static bigarray* ptr = NULL;
if (ptr == NULL) {
ptr = new float[100][100][100];
for(int j=0; j<100; j++) {
ptr[j] = new float[100][100];
for(int i=0; i<100; i++)
ptr[j][i] = new float[100];
}
}
return *ptr;
}
That will allocate the structure in dynamic memory the first time it is accessed, as a jagged array. You can get more performance out of a rectangle array, but you have to change types:
typedef std::vector<std::array<std::array<float, 100>, 100> bigarray;
bigarray TC(100);
According to http://cs.nyu.edu/exact/core/doc/stackOverflow.txt, gcc/linux defaults the stack size to 8MB, which isn't big enough for your structure and int main() If you really want to, MSVC has flags to increase the stack sizes up to 32MB. Linux has a ulimit command to increase the stack size up to 32MB.