Is There a Max Array Length Limit in C++

What is the maximum size of an array in C?

There is no fixed limit to the size of an array in C.

The size of any single object, including of any array object, is limited by SIZE_MAX, the maximum value of type size_t, which is the result of the sizeof operator. (It's not entirely clear whether the C standard permits objects larger than SIZE_MAX bytes, but in practice such objects are not supported; see footnote.) Since SIZE_MAX is determined by the implementation, and cannot be modified by any program, that imposes an upper bound of SIZE_MAX bytes for any single object. (That's an upper bound, not a least upper bound; implementations may, and typically do, impose smaller limits.)

The width of the type void*, a generic pointer type, imposes an upper bound on the total size of all objects in an executing program (which may be larger than the maximum size of a single object).

The C standard imposes lower bounds, but not upper bounds, on these fixed sizes. No conforming C implementation can support infinite-sized objects, but it can in principle support objects of any finite size. Upper bounds are imposed by individual C implementations, by the environments in which they operate, and by physics, not by the language.

For example, a conforming implementation could have SIZE_MAX equal to 2¹⁰²⁴-1, which means it could in principle have objects up to 179769313486231590772930519078902473361797697894230657273430081157732675805500963132708477322407536021120113879871393357658789768814416622492847430639474124377767893424865485276302219601246094119453082952085005768838150682342462881473913110540827237163350510684586298239947245938479716304835356329624224137215 bytes.

Good luck finding hardware that actually supports such objects.

Footnote: There is no explicit rule that no object can be bigger than SIZE_MAX bytes. You couldn't usefully apply the sizeof operator to such an object, but like any other operator, sizeof can overflow; that doesn't mean you couldn't perform operations on such an object. But in practice, any sane implementation will make size_t big enough to represent the size of any object it supports.

Is there a max array length limit in C++?

There are two limits, both not enforced by C++ but rather by the hardware.

The first limit (should never be reached) is set by the restrictions of the size type used to describe an index in the array (and the size thereof). It is given by the maximum value the system's std::size_t can take. This data type is large enough to contain the size in bytes of any object

The other limit is a physical memory limit. The larger your objects in the array are, the sooner this limit is reached because memory is full. For example, a vector<int> of a given size n typically takes multiple times as much memory as an array of type vector<char> (minus a small constant value), since int is usually bigger than char. Therefore, a vector<char> may contain more items than a vector<int> before memory is full. The same counts for raw C-style arrays like int[] and char[].

Additionally, this upper limit may be influenced by the type of allocator used to construct the vector because an allocator is free to manage memory any way it wants. A very odd but nontheless conceivable allocator could pool memory in such a way that identical instances of an object share resources. This way, you could insert a lot of identical objects into a container that would otherwise use up all the available memory.

Apart from that, C++ doesn't enforce any limits.

Is there a limit on array size in C?

You are using VLAs as automatic variables allocated on your call stack. So you are limited by the call stack maximal size (often only a few megabytes, details are OS and computer specific).

You should instead allocate these on the heap. Read about C dynamic memory allocation. So code instead

long long *num_operations = calloc (n + 1, sizeof(long long));
long long *sequence = calloc(n, sizeof(long long));

Don't forget to test for failure of calloc:

if (!num_operations) 
    { perror("num_operations calloc"); exit(EXIT_FAILURE); }

and likewise for the calloc of sequence

Don't forget to free (e.g. at end of your main)

free (num_operations);
free (sequence);

to avoid memory leaks (use valgrind to debug these). In your particular case, you might not free since the virtual address space of a program (on Linux or Windows, etc...) is deleted when its process is ended.

FYI malloc, calloc, and free are using system calls, such as mmap(2), to change the virtual address space. But often the C standard library don't release (using munmap) free-d memory to the OS but marks it as reusable by future malloc-s or calloc-s.

In practice, you'll better free memory as soon as it becomes unneeded (so you often can calloc and free in the same routine). Reading about garbage collection techniques, concepts, and terminology is worthwhile.

Of course, heap allocated memory is also limited (since your computer has finite resources), but the limit could depend on the computer and is typically much bigger (at least gigabytes on a laptop, and probably terabytes on supercomputers); sometimes calloc appear to work (read about memory overcommitment) even when resources are exhausted (this is an OS feature I generally disable). On POSIX and Linux systems setrlimit(2) could be used to lower (or change a bit) that limit.

Is there any limitation on the maximum size of array in c?

I am guessing that idata is a local variable. The problem is that local variables are stored on the stack (technically "automatic storage"), and the stack is much smaller than the 6400 megabytes you're trying to allocate on it. Allocating that much storage on it causes a stack overflow.

Try

unsigned char** idata = new unsigned char*[DIM1];

for (int i = 0; i < DIM1; ++i)
    idata[i] = new unsigned char[DIM2];

// or

unsigned char (*idata)[DIM2] = new char[DIM1][DIM2];

To allocate it in the free store and you shouldn't have a problem.

EDIT:

I just looked at the tags and didn't see you were only talking about C. If so, you can do the same thing but use malloc instead of new:

unsigned char** idata = malloc(sizeof(unsigned char*) * DIM1);

for (i = 0; i < DIM1; ++i)
    idata[i] = malloc(DIM2);

// or

unsigned char (*idata)[DIM2] = malloc(DIM1 * DIM2);

And don't forget to free (or delete[] for C++) the memory you allocate to avoid memory leaks.

C++ C-style array size limit

Does anyone have an idea where this limit comes

It comes fromn the language implementation. The space available for automatic storage is typically limited to one or few megabytes (potentially less on embedded systems) and that space is shared with all automatic variables on the same thread of execution.

Since this area of memory is called the stack, the crash that you are experiencing is called a stack overflow.

how I can overcome it?

Use dynamic or static storage instead of automatic for large objects.

What is the Maximum Size that an Array can hold?

System.Int32.MaxValue

Assuming you mean System.Array, ie. any normally defined array (int[], etc). This is the maximum number of values the array can hold. The size of each value is only limited by the amount of memory or virtual memory available to hold them.

This limit is enforced because System.Array uses an Int32 as it's indexer, hence only valid values for an Int32 can be used. On top of this, only positive values (ie, >= 0) may be used. This means the absolute maximum upper bound on the size of an array is the absolute maximum upper bound on values for an Int32, which is available in Int32.MaxValue and is equivalent to 2^31, or roughly 2 billion.

On a completely different note, if you're worrying about this, it's likely you're using alot of data, either correctly or incorrectly. In this case, I'd look into using a List<T> instead of an array, so that you are only using as much memory as needed. Infact, I'd recommend using a List<T> or another of the generic collection types all the time. This means that only as much memory as you are actually using will be allocated, but you can use it like you would a normal array.

The other collection of note is Dictionary<int, T> which you can use like a normal array too, but will only be populated sparsely. For instance, in the following code, only one element will be created, instead of the 1000 that an array would create:

Dictionary<int, string> foo = new Dictionary<int, string>();
foo[1000] = "Hello world!";
Console.WriteLine(foo[1000]);

Using Dictionary also lets you control the type of the indexer, and allows you to use negative values. For the absolute maximal sized sparse array you could use a Dictionary<ulong, T>, which will provide more potential elements than you could possible think about.

Is there an upper limit on size of an array in a c++ array container?

If it's a global variable, then it's most likely only limited by the amount of memory your process can use [in other words, how much memory your machine has, and that the OS lets the process have, whichever is lower].

If it's a local variable inside a function (and the "bad access" seen in your error message indicates that this is case, but it's not clear from your code samples), since std::array takes space on the stack, the limit is whatever your stack-size is. If you want a LOCAL variable to hold a lot of items, use std::vector, which will dynamically allocate, and then becomes limited by the amount of memory in your machine [as per above].

There are many other ways to solve this problem, but std::vector<double> A1(ARRAY_SIZE); is the simplest version, and it will only require one single call to new double[ARRAY_SIZE]; which is likely to not be noticeable in your overall run time if you fill and sort the contents of 1 million entries.

Maximum Index of an array and it's length on a platform

Objects

The largest size of an object is about SIZE_MAX. sizeof object returns the size of any object. The type returned is type size_t. The range of size_t is [0...SIZE_MAX].

The size limit is effective one less as the address after the object needs to be computable.

Since an array is an object, the largest 4-byte int array would be

int big_int_array[SIZE_MAX/sizeof(int)];  // Perhaps 1 less

Allocations

The largest memory that be be allocated via malloc() is about SIZE_MAX.

char *big_array = malloc(SIZE_MAX - 1);

The largest memory that be be allocated via calloc() is about SIZE_MAX * SIZE_MAX bytes, yet such a large allocation attempts usually return NULL.

double *big_array = calloc(SIZE_MAX/2, sizeof *big_array);

Rare machines allows this, not Linux. Most platforms will returns NULL if the product meets/exceeds SIZE_MAX.

Here, big_array[] can be indexed [0...SIZE_MAX/2). This usually requires the address scheme to not be the traditional universal linear model many platforms employ.