I'm using std::bitset and trying to create two arrays std::bitset with size 100,000,000,000


I am using std::bitset and I try to create two arrays std::bitset with size 100,000,000,000. As a result, program fills only 298 MB of my RAM but must to fill ~24 GB. I have 32 GB RAM and now 26 GB are free. When I build my code for x86, it compiles and can start but for x64 it shows me the following: error C2148: total size of array must not exceed 0x7fffffff bytes. How to fix it and do not reduce size of bitset arrays?

I have tried to make 2 global arrays. Also, I have set in Microsoft visual studio -> project -> name_project properties -> configuration properties -> linker -> system -> Stack Reserve Size to 25,000,000 (i think that there must be KB, so i think i have set to ~25 GB).

... // other libraries
#include <bitset>

std::bitset <100000000000>mas;
std::bitset <100000000000>a1;

int main() {.../* work with the arrays */...}

I want to run the code with the huge std::bitset arrays.

UPD: for x86 ok, but what for x64? my code checks whole arrays and at one moment it stops.

asked on Stack Overflow Sep 11, 2019 by kileatb • edited Sep 11, 2019 by kileatb

1 Answer


std::bitset must, at a minimum (and most implementations use the minimum), use one byte per eight bits to be stored. For 100 billion bits, that means you need ~12.5 GB of memory per bitset. Problem is, on a 32 bit system, your maximum virtual memory size for the whole program is at most 4 GB. Some of that is eaten by the kernel memory reservation for the process, so odds are you only have 2 GB of virtual address space to use; you're trying to use six times that much.

Your program cannot run on a 32 bit system without shrinking the bitset. If it claims to run, it's likely a different error; it would be truncating 100_000_000_000 to fit in a 32 bit size_t, creating a std::bitset<1215752192> instead, which would only require ~150 MB of memory, causing no problems. That would explain your observed memory usage of 298 MB; the memory usage display uses "mebibytes" (base-2, not base-10, so KiB == 1024 and MiB == 1048576), which makes each array consume just under 145 MiB, 290 MiB total for two of them, leaving 8 MiB for the rest of your program (which seems reasonable).

If it is in fact dying on x64 with that error, you're stuck; whoever implemented your std::bitset (or whatever data structure backs it, e.g. std::array) limited it to 0x7fffffff bytes even on a 64 bit system, which would limit you to std::bitsets of around 17 billion bits or less. Your only option would be to find a different provider for your standard library, or reimplement it yourself.

Update: Apparently you're using Windows, and the limit on static data size is 2GB (0x7fffffff bytes), even on 64 bit Windows; the Windows Portable Executable file format (used by .exe and .dll files) uses 32 bit offsets and lengths for each section, even for 64 bit executables. By using global std::bitsets, you're trying to store 25 GB of static data in the image, which won't work. Moving them to the stack (declaring them non-static inside the body of main) might work if you increase the Stack Reserve Size like you did, but it's still a bad idea to rely on a stack that large. I'd suggest simply dynamically allocating the bitset (e.g. auto mas = std::make_unique<std::bitset<100000000000>>()), or finding a better way to do this with a smaller bitset.

answered on Stack Overflow Sep 11, 2019 by ShadowRanger • edited Sep 11, 2019 by ShadowRanger

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