Performs the following operations in order:

1. Implicitly creates objects atdest.
2. Copiescount characters (as if of typeunsignedchar) from the object pointed to bysrc into the object pointed to bydest.

If any of the following conditions is satisfied, the behavior is undefined:

• dest orsrc is anull pointer orinvalid pointer.
• Copying takes place between objects that overlap.

[edit]Parameters

[edit]Return value

If there is asuitable created object, returns a pointer to it; otherwise returnsdest.

[edit]Notes

std::memcpy is meant to be the fastest library routine for memory-to-memory copy. It is usually more efficient thanstd::strcpy, which must scan the data it copies orstd::memmove, which must take precautions to handle overlapping inputs.

Several C++ compilers transform suitable memory-copying loops tostd::memcpy calls.

Wherestrict aliasing prohibits examining the same memory as values of two different types,std::memcpy may be used to convert the values.

[edit]Example

#include <cstdint>#include <cstring>#include <iostream> int main(){// simple usagechar source[]="once upon a daydream...", dest[4];    std::memcpy(dest, source, sizeof dest);std::cout<<"dest[4] = {";for(int n{};char c: dest)std::cout<<(n++?", ":"")<<'\''<< c<<"'";std::cout<<"};\n"; // reinterpretingdouble d=0.1;//  std::int64_t n = *reinterpret_cast<std::int64_t*>(&d); // aliasing violationstd::int64_t n;    std::memcpy(&n,&d, sizeof d);// OK std::cout<<std::hexfloat<< d<<" is "<<std::hex<< n<<" as a std::int64_t\n"<<std::dec; // object creation in destination bufferstruct S{int x{42};void print()const{std::cout<<'{'<< x<<"}\n";}} s;    alignas(S)char buf[sizeof(S)];    S* ps= new(buf) S;// placement new    std::memcpy(ps,&s, sizeof s);    ps->print();}

dest[4] = {'o', 'n', 'c', 'e'};0x1.999999999999ap-4 is 3fb999999999999a as a std::int64_t{42}

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

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