A Boost C++ library that provides a container that can represent uninitialized objects of arbitrary type, notably allowing easier definition of functions that might not have a value to return
Questions tagged [boost-optional]
100 questions
3
votes
2 answers
Boost::optional dereference
I am reviewing some code and have something like this:
boost::optional isSet = ...;
... some code goes here...
bool smthelse = isSet ? *isSet : false;
So my question is, is the last line equivalent to this:
bool smthelse = isSet;
Eduard Rostomyan
- 7,050
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3
votes
1 answer
Do optional references in c++ preserve object life?
Say I have:
#include
#include "boost/optional.hpp"
struct cat
{
int paw = 4;
};
int main()
{
boost::optional z;
{
cat realCat = cat();
z = realCat;
}
std::cout << z->paw << std::endl;
return…
Carbon
- 3,828
- 3
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3
votes
3 answers
C2143 syntax error when including boost/optional.hpp
I'm stuck with a compile-time error which I cannot understand. I try to use boost::optional in my code, and as soon as I include boost/optional.hpp I cannot build my project any longer. If I comment this include statement out, it works. I don't even…
Software Craftsman
- 2,999
- 2
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- 47
3
votes
1 answer
Can I safely point to the data of a reassigned boost::optional?
Given the following code sample:
boost::optional< int > opt;
opt = 12;
int* p( &*opt );
opt = 24;
assert( p == &*opt );
Is there any guarantee that the assert will always be valid?
Julien
- 2,139
- 1
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3
votes
3 answers
Viewing a raw pointer as a range in range-based for-loop
How can I make a raw pointer behave like a range, for a for-range loop syntax.
double five = 5;
double* dptr = &five;
for(int& d : dptr) std::cout << d << std::endl;// will not execute if the pointer is null
Motivation:
It is now vox populi that an…
alfC
- 14,261
- 4
- 67
- 118
3
votes
1 answer
how to divide boost::optional?
I have such code:
boost::optional result = _ind1.Value() / _ind2.Value();
Each arg is boost::optional too:
boost::optional Value() {
return value;
}
Errors are:
Error 1 error C2676: binary '/' : 'boost::optional'…
Oleg Vazhnev
- 23,239
- 54
- 171
- 305
3
votes
2 answers
How can I make sure a boost::optional object is initialized in release-build?
When trying to get the value of a boost::optional object, BOOST_ASSERT is used to make sure the object is indeed initialized.
But what I would like when dereferencing an uninitialized optional is for an exception to be thrown - is there any way to…
Danra
- 9,546
- 5
- 59
- 117
2
votes
3 answers
How to decay rvalues reference type whilst preserving lvalue references in C++14?
I have the following C++14 lambda
https://godbolt.org/z/aexxTY
#include
int main(){
auto foo = [](auto && t)
{
using T = decltype(t);
return boost::optional(std::forward(t));
};
// This…
bradgonesurfing
- 30,949
- 17
- 114
- 217
2
votes
1 answer
How to rewrite with boost::optional in C++11?
How do I rewrite the following code to use boost::optional or boost::none, in C++11?
std::unique_ptr find( std::string key)
{
std::map(void)> > m{
{"key1",…
javauser
- 31
- 1
2
votes
1 answer
How to forward constructor arguments to boost::optional
I have the following simple struct:
struct X
{
X(std::string name, int value): name_(name), value_(value){}
std::string name_;
int value_;
};
I would like to use it with boost optional without copying. Here is one…
Irbis
- 1,432
- 1
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- 39
2
votes
2 answers
Why does this use of boost::none fail to compile with nvcc?
I'm trying to compile the following code:
#include
void foo(boost::optional x = boost::none);
placed in the file a.cu, with the CUDA compiler, using the following command line:
nvcc a.cu -c --std=c++11…
einpoklum
- 118,144
- 57
- 340
- 684
2
votes
0 answers
nlohmann json ambiguous overload for 'operator='
I'm getting this compilation error with the following code
#include
#include
#include "nlohmann_json.hpp"
namespace nlohmann {
template
struct adl_serializer> {
static void…
SU3
- 5,064
- 3
- 35
- 66
2
votes
2 answers
Do std::optional and boost::optional respect alignment restrictions of the managed object?
If a class T has an alignment requirement, such as one specified by the alignas keyword, are std::optional and boost::optional guaranteed to respect said alignment?
If they were simply wrapper classes for a T object and a bool initialized,…
patatahooligan
- 3,111
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2
votes
1 answer
How to properly use boost::program_options::implicit_value for vector of string?
Proof of code:
boost::program_options::options_description options;
Parser::Parser(): options("Allowed options")
{
options.add_options()
("help,h", "produce help message")
("type,t", po::value()->required()->implicit_value(""),…
andrew
- 3,083
- 4
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- 29
2
votes
1 answer
Boost Optional with Boost Thread compilation issue
My environment is Visual Stuido 2013, VC12, Boost 1.59.
The following code (a minimal repro of the real code):
#include "boost/thread.hpp"
#include "boost/optional.hpp"
class MyClass
{
public:
template
operator const T& ()…
Greg Ravikovich
- 45
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