Declaring a very large vector of ints?

Question

Is there a way to do this in C++ without having things crash on runtime?

Right now I am declaring

vector<vector<int> > myvec(veclength);

How can I crank up veclength as high as it will go (properly)? Even at 10^7 it crashes when I should have more than enough computer memory.

Answer 1

This should take take approximately 250 MiB of space¹ (or less, depending on architecture) so memory definitely isn’t the problem here, and neither should max_size, which would be in the order of 10¹⁷ (≈ ²⁶⁴∕₈₊₈₊₈).

I should mention that I corroborated these calculations by looking at the implementations of std::vectorin GCC' libstdc++ and LLVM's libc++, and by testing on a live system. The calculated values correspond 1:1 to the real implementations, and the OP’s code works flawlessly with veclength = 10e7.

I therefore conclude that the real cause is elsewhere.

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¹⁾ Calculated by approximating the size of each individual vector by three 64 bit integers to denote begin pointer, size and capacity respectively, and assuming that an empty vector has a default capacity of 0. Actual implementations may differ but probably not by much.