NAME¶

std::experimental::make_unique_resource_checked - std::experimental::make_unique_resource_checked

Synopsis¶

Defined in header <experimental/scope>
template <class R, class D, class S = std::decay_t<R>>

std::experimental::unique_resource<std::decay_t<R>, (library
std::decay_t<D>> fundamentals TS v3)
make_unique_resource_checked(R&& r, const S& invalid, D&& d)

noexcept(/*see below*/);

Creates a unique_resource, initializes its stored resource handle is initialized
with std::forward<R>(r) and its deleter with std::forward<D>(d). The created
unique_resource owns the resource if and only if bool(r == invalid) is false.

The program is ill-formed if the expression r == invalid cannot be contextually
converted to bool, and the behavior is undefined if the conversion results in
undefined behavior or throws an exception.

Paramaters

r - a resouce handle
d - a deleter to use to dispose the resource
invalid - a value indicating the resource handle is invalid

Reture value

A unique_resource described above.

Exceptions¶

Any exception thrown in initialization of the stored resource handle and the
deleter.

noexcept specification:
noexcept(

std::is_nothrow_constructible_v<std::decay_t<R>, R> &&
std::is_nothrow_constructible_v<std::decay_t<D>, D>

)

Notes¶

make_unique_resource_checked exists to avoid calling a deleter function with an
invalid argument.

Resource handle r is either copied or moved into the return value, and the created
unique_resource always holds an underlying resource handle with object type.

Example¶

// Run this code

#include <cstdio>
#include <experimental/scope>

int main()
{
// avoid calling fclose when fopen fails
auto file = std::experimental::make_unique_resource_checked(
std::fopen("potentially_nonexistent_file.txt", "r"),
nullptr,
[](std::FILE *fptr){ std::fclose(fptr); }
);
if (file.get()) {
std::puts("The file exits.");
}
else {
std::puts("The file does not exist.");
}
}

Possible output:¶

The file does not exist.

See also¶