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

Question

Is there a max length for an array in C++?

Is it a C++ limit or does it depend on my machine? Is it tweakable? Does it depend on the type the array is made of?

Answer 1

As many excellent answers noted, there are a lot of limits that depend on your version of C++ compiler, operating system and computer characteristics. However, I suggest the following script on Python that checks the limit on your machine.

It uses binary search and on each iteration checks if the middle size is possible by creating a code that attempts to create an array of the size. The script tries to compile it (sorry, this part works only on Linux) and adjust binary search depending on the success. Check it out:

import os

cpp_source = 'int a[{}]; int main() {{ return 0; }}'

def check_if_array_size_compiles(size):
        #  Write to file 1.cpp
        f = open(name='1.cpp', mode='w')
        f.write(cpp_source.format(m))
        f.close()
        #  Attempt to compile
        os.system('g++ 1.cpp 2> errors')
        #  Read the errors files
        errors = open('errors', 'r').read()
        #  Return if there is no errors
        return len(errors) == 0

#  Make a binary search. Try to create array with size m and
#  adjust the r and l border depending on wheather we succeeded
#  or not
l = 0
r = 10 ** 50
while r - l > 1:
        m = (r + l) // 2
        if check_if_array_size_compiles(m):
                l = m
        else:
                r = m

answer = l + check_if_array_size_compiles(r)
print '{} is the maximum avaliable length'.format(answer)

You can save it to your machine and launch it, and it will print the maximum size you can create. For my machine it is 2305843009213693951.