#Is there a function that returns an aligned pointer for some T in a buffer?

26 messages · Page 1 of 1 (latest)

potent wing
#

so, what I need is

char buff [1024]; // alignment is 1
char* start = buff+7;
T* alignedPtr = find_aligned_in_buff<T>(start, buff, 1024); //alignment must be alignof(T), if no such pointer exists after start in the buffer nullptr must be returned

does the standard library have something like this? or do I need to manually make it myself?

whole atlasBOT
#

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potent wing
#

this is used to store different variables of type T1, T2, etc... inside a single char buffer of course,
the easy way out would be just to use std::tuple<T1,T2, etc...> and call it a day, but I want to do it manually because std::tuple will call destructors, I do not want to call them immideately

#

hold up... is there a placement aligned operator new ?

eternal scaffold
#

std::align?

potent wing
potent wing
# eternal scaffold std::align? 
#include <iostream>
#include <memory>

class alignas(256) Demo
{
    char data[10];
};

int main() {
     char arr[1024] = {};
     
     void* result = arr;
     size_t buffLen = 1024;
    
     bool success = std::align(alignof(Demo), sizeof(Demo), result, buffLen) != nullptr;

    std::cout<<"success? "<<(success ? "yes" : "no")<<"\n";
    std::cout<<"buffer begin = "<<((void*)&arr[0])<<"\n";
    std::cout<<"buffer end = "<<((void*)&arr[1024])<<"\n";
    std::cout<<"aligned result begin: "<<result<<"\n";
    std::cout<<"aligned result end: "<<(void*)((char*)result + buffLen)<<"\n";
    std::cout<<"new buffer length = "<<buffLen<<"\n";
}

is this how it works?

#

it will try to find an address starting from the pointer result ?

#

and adjust result and buffLen accordingly?

ripe stirrup
potent wing
ripe stirrup
eternal scaffold
potent wing
#

!solved

whole atlasBOT
#

Thank you and let us know if you have any more questions!

eternal scaffold
potent wing
eternal scaffold
#

the standard specification is actually workable in this case ^^

potent wing
#

it would have been great for my teachers to tell us that this thing exists in C++11 right after they taught us about alignof, but they did not, I had to manually do this from scratch when writing a FirstFit, BestFit and WorstFit memory allocator

#

and also explaining that you are not supposed to do void* + size_t, even though -O3 allows it

eternal scaffold