Initialise a reference member to C array don't compile on visual studio 2015












2















When I try to compile the code below on g++ it's work but on vs2015 it's fail with message :
error C2440: 'initializing': cannot convert from 'const bool *' to 'const bool (&)[3]'



#include <iostream>

enum class Direction
{
RIGTH,
LEFT
};

struct Buffer
{
int catRigth = 4;
int catLeft = 8;
bool dogRigth[3] = {true, false, true};
bool dogLeft[3] = {false, true, false};
};

struct Bind
{
const int &cat;
const bool (&dog)[3];
Bind(const Buffer &buf, Direction direction) :
cat(direction == Direction::RIGTH ? buf.catRigth : buf.catLeft),
dog(direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)
{
}
};

int main(int argc, char* argv)
{

const Buffer buff;

Bind bindRigth(buff, Direction::RIGTH);
Bind bindLeft(buff, Direction::LEFT);

int catRigth = bindRigth.cat;
int catLeft = bindLeft.cat;

std::cout << catRigth << " " << catLeft;
}


Is it a standard C++ code or it's gcc specific comportment?










share|improve this question

























  • Or in other words: does the conditional operator trigger array-to-pointer decay?

    – Quentin
    Nov 23 '18 at 10:38











  • Seems like only MSVC has this behavior. clang, gcc and icc work as "expected"

    – Matthieu Brucher
    Nov 23 '18 at 10:39











  • Initialize it like this: _dog { direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)} {}

    – snake_style
    Nov 23 '18 at 11:03













  • Tried your code out on cpp.sh, it complained about obj not being initialized. Did that, worked then. Maybe doing that makes it work on vs2015 too? (Altered code: cpp.sh/3wqyg ) In any case ugly code, why don't you simply use a pointer?

    – Aziuth
    Nov 23 '18 at 11:39













  • Sorry I accepted the edit by Felix when I probably don't do, I'm new here. I tested my code on real vs and it don't compiled.

    – Gurdil
    Nov 23 '18 at 11:57


















2















When I try to compile the code below on g++ it's work but on vs2015 it's fail with message :
error C2440: 'initializing': cannot convert from 'const bool *' to 'const bool (&)[3]'



#include <iostream>

enum class Direction
{
RIGTH,
LEFT
};

struct Buffer
{
int catRigth = 4;
int catLeft = 8;
bool dogRigth[3] = {true, false, true};
bool dogLeft[3] = {false, true, false};
};

struct Bind
{
const int &cat;
const bool (&dog)[3];
Bind(const Buffer &buf, Direction direction) :
cat(direction == Direction::RIGTH ? buf.catRigth : buf.catLeft),
dog(direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)
{
}
};

int main(int argc, char* argv)
{

const Buffer buff;

Bind bindRigth(buff, Direction::RIGTH);
Bind bindLeft(buff, Direction::LEFT);

int catRigth = bindRigth.cat;
int catLeft = bindLeft.cat;

std::cout << catRigth << " " << catLeft;
}


Is it a standard C++ code or it's gcc specific comportment?










share|improve this question

























  • Or in other words: does the conditional operator trigger array-to-pointer decay?

    – Quentin
    Nov 23 '18 at 10:38











  • Seems like only MSVC has this behavior. clang, gcc and icc work as "expected"

    – Matthieu Brucher
    Nov 23 '18 at 10:39











  • Initialize it like this: _dog { direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)} {}

    – snake_style
    Nov 23 '18 at 11:03













  • Tried your code out on cpp.sh, it complained about obj not being initialized. Did that, worked then. Maybe doing that makes it work on vs2015 too? (Altered code: cpp.sh/3wqyg ) In any case ugly code, why don't you simply use a pointer?

    – Aziuth
    Nov 23 '18 at 11:39













  • Sorry I accepted the edit by Felix when I probably don't do, I'm new here. I tested my code on real vs and it don't compiled.

    – Gurdil
    Nov 23 '18 at 11:57
















2












2








2








When I try to compile the code below on g++ it's work but on vs2015 it's fail with message :
error C2440: 'initializing': cannot convert from 'const bool *' to 'const bool (&)[3]'



#include <iostream>

enum class Direction
{
RIGTH,
LEFT
};

struct Buffer
{
int catRigth = 4;
int catLeft = 8;
bool dogRigth[3] = {true, false, true};
bool dogLeft[3] = {false, true, false};
};

struct Bind
{
const int &cat;
const bool (&dog)[3];
Bind(const Buffer &buf, Direction direction) :
cat(direction == Direction::RIGTH ? buf.catRigth : buf.catLeft),
dog(direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)
{
}
};

int main(int argc, char* argv)
{

const Buffer buff;

Bind bindRigth(buff, Direction::RIGTH);
Bind bindLeft(buff, Direction::LEFT);

int catRigth = bindRigth.cat;
int catLeft = bindLeft.cat;

std::cout << catRigth << " " << catLeft;
}


Is it a standard C++ code or it's gcc specific comportment?










share|improve this question
















When I try to compile the code below on g++ it's work but on vs2015 it's fail with message :
error C2440: 'initializing': cannot convert from 'const bool *' to 'const bool (&)[3]'



#include <iostream>

enum class Direction
{
RIGTH,
LEFT
};

struct Buffer
{
int catRigth = 4;
int catLeft = 8;
bool dogRigth[3] = {true, false, true};
bool dogLeft[3] = {false, true, false};
};

struct Bind
{
const int &cat;
const bool (&dog)[3];
Bind(const Buffer &buf, Direction direction) :
cat(direction == Direction::RIGTH ? buf.catRigth : buf.catLeft),
dog(direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)
{
}
};

int main(int argc, char* argv)
{

const Buffer buff;

Bind bindRigth(buff, Direction::RIGTH);
Bind bindLeft(buff, Direction::LEFT);

int catRigth = bindRigth.cat;
int catLeft = bindLeft.cat;

std::cout << catRigth << " " << catLeft;
}


Is it a standard C++ code or it's gcc specific comportment?







c++ visual-studio-2015






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited Nov 23 '18 at 12:23







Gurdil

















asked Nov 23 '18 at 10:33









GurdilGurdil

135




135













  • Or in other words: does the conditional operator trigger array-to-pointer decay?

    – Quentin
    Nov 23 '18 at 10:38











  • Seems like only MSVC has this behavior. clang, gcc and icc work as "expected"

    – Matthieu Brucher
    Nov 23 '18 at 10:39











  • Initialize it like this: _dog { direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)} {}

    – snake_style
    Nov 23 '18 at 11:03













  • Tried your code out on cpp.sh, it complained about obj not being initialized. Did that, worked then. Maybe doing that makes it work on vs2015 too? (Altered code: cpp.sh/3wqyg ) In any case ugly code, why don't you simply use a pointer?

    – Aziuth
    Nov 23 '18 at 11:39













  • Sorry I accepted the edit by Felix when I probably don't do, I'm new here. I tested my code on real vs and it don't compiled.

    – Gurdil
    Nov 23 '18 at 11:57





















  • Or in other words: does the conditional operator trigger array-to-pointer decay?

    – Quentin
    Nov 23 '18 at 10:38











  • Seems like only MSVC has this behavior. clang, gcc and icc work as "expected"

    – Matthieu Brucher
    Nov 23 '18 at 10:39











  • Initialize it like this: _dog { direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)} {}

    – snake_style
    Nov 23 '18 at 11:03













  • Tried your code out on cpp.sh, it complained about obj not being initialized. Did that, worked then. Maybe doing that makes it work on vs2015 too? (Altered code: cpp.sh/3wqyg ) In any case ugly code, why don't you simply use a pointer?

    – Aziuth
    Nov 23 '18 at 11:39













  • Sorry I accepted the edit by Felix when I probably don't do, I'm new here. I tested my code on real vs and it don't compiled.

    – Gurdil
    Nov 23 '18 at 11:57



















Or in other words: does the conditional operator trigger array-to-pointer decay?

– Quentin
Nov 23 '18 at 10:38





Or in other words: does the conditional operator trigger array-to-pointer decay?

– Quentin
Nov 23 '18 at 10:38













Seems like only MSVC has this behavior. clang, gcc and icc work as "expected"

– Matthieu Brucher
Nov 23 '18 at 10:39





Seems like only MSVC has this behavior. clang, gcc and icc work as "expected"

– Matthieu Brucher
Nov 23 '18 at 10:39













Initialize it like this: _dog { direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)} {}

– snake_style
Nov 23 '18 at 11:03







Initialize it like this: _dog { direction == Direction::RIGTH ? buf.dogRigth : buf.dogLeft)} {}

– snake_style
Nov 23 '18 at 11:03















Tried your code out on cpp.sh, it complained about obj not being initialized. Did that, worked then. Maybe doing that makes it work on vs2015 too? (Altered code: cpp.sh/3wqyg ) In any case ugly code, why don't you simply use a pointer?

– Aziuth
Nov 23 '18 at 11:39







Tried your code out on cpp.sh, it complained about obj not being initialized. Did that, worked then. Maybe doing that makes it work on vs2015 too? (Altered code: cpp.sh/3wqyg ) In any case ugly code, why don't you simply use a pointer?

– Aziuth
Nov 23 '18 at 11:39















Sorry I accepted the edit by Felix when I probably don't do, I'm new here. I tested my code on real vs and it don't compiled.

– Gurdil
Nov 23 '18 at 11:57







Sorry I accepted the edit by Felix when I probably don't do, I'm new here. I tested my code on real vs and it don't compiled.

– Gurdil
Nov 23 '18 at 11:57














1 Answer
1






active

oldest

votes


















1














MSVC shouldn't have decayed its type to const bool *:




5.16.4 If the second and third operands are glvalues of the same value category and have the same type, the result is of that type and value category and it is a bit-field if the second or the third operand is a bit-field, or if both are bit-fields.




A workaround for MSVC could be:



#include <utility>

const struct A {
bool a[3] = {false};
} obj;

template <class Lhs, class Rhs>
auto &&Conditional(const bool x, Lhs &&lhs, Rhs &&rhs) {
if (x)
return std::forward<Lhs>(lhs);
return std::forward<Rhs>(rhs);
}

int main(int argc, char* argv) {
const bool (&t)[3] = Conditional(true, obj.a, obj.a);
return 0;
}


PS: Conditional isn't a constexpr function.



Or: const bool (&t)[3] = *(true ? &obj.a : &obj.a);






share|improve this answer


























  • Thanks your solution to reference on ternary and dereference the result do the job for me

    – Gurdil
    Nov 23 '18 at 13:01











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1 Answer
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1 Answer
1






active

oldest

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active

oldest

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active

oldest

votes









1














MSVC shouldn't have decayed its type to const bool *:




5.16.4 If the second and third operands are glvalues of the same value category and have the same type, the result is of that type and value category and it is a bit-field if the second or the third operand is a bit-field, or if both are bit-fields.




A workaround for MSVC could be:



#include <utility>

const struct A {
bool a[3] = {false};
} obj;

template <class Lhs, class Rhs>
auto &&Conditional(const bool x, Lhs &&lhs, Rhs &&rhs) {
if (x)
return std::forward<Lhs>(lhs);
return std::forward<Rhs>(rhs);
}

int main(int argc, char* argv) {
const bool (&t)[3] = Conditional(true, obj.a, obj.a);
return 0;
}


PS: Conditional isn't a constexpr function.



Or: const bool (&t)[3] = *(true ? &obj.a : &obj.a);






share|improve this answer


























  • Thanks your solution to reference on ternary and dereference the result do the job for me

    – Gurdil
    Nov 23 '18 at 13:01
















1














MSVC shouldn't have decayed its type to const bool *:




5.16.4 If the second and third operands are glvalues of the same value category and have the same type, the result is of that type and value category and it is a bit-field if the second or the third operand is a bit-field, or if both are bit-fields.




A workaround for MSVC could be:



#include <utility>

const struct A {
bool a[3] = {false};
} obj;

template <class Lhs, class Rhs>
auto &&Conditional(const bool x, Lhs &&lhs, Rhs &&rhs) {
if (x)
return std::forward<Lhs>(lhs);
return std::forward<Rhs>(rhs);
}

int main(int argc, char* argv) {
const bool (&t)[3] = Conditional(true, obj.a, obj.a);
return 0;
}


PS: Conditional isn't a constexpr function.



Or: const bool (&t)[3] = *(true ? &obj.a : &obj.a);






share|improve this answer


























  • Thanks your solution to reference on ternary and dereference the result do the job for me

    – Gurdil
    Nov 23 '18 at 13:01














1












1








1







MSVC shouldn't have decayed its type to const bool *:




5.16.4 If the second and third operands are glvalues of the same value category and have the same type, the result is of that type and value category and it is a bit-field if the second or the third operand is a bit-field, or if both are bit-fields.




A workaround for MSVC could be:



#include <utility>

const struct A {
bool a[3] = {false};
} obj;

template <class Lhs, class Rhs>
auto &&Conditional(const bool x, Lhs &&lhs, Rhs &&rhs) {
if (x)
return std::forward<Lhs>(lhs);
return std::forward<Rhs>(rhs);
}

int main(int argc, char* argv) {
const bool (&t)[3] = Conditional(true, obj.a, obj.a);
return 0;
}


PS: Conditional isn't a constexpr function.



Or: const bool (&t)[3] = *(true ? &obj.a : &obj.a);






share|improve this answer















MSVC shouldn't have decayed its type to const bool *:




5.16.4 If the second and third operands are glvalues of the same value category and have the same type, the result is of that type and value category and it is a bit-field if the second or the third operand is a bit-field, or if both are bit-fields.




A workaround for MSVC could be:



#include <utility>

const struct A {
bool a[3] = {false};
} obj;

template <class Lhs, class Rhs>
auto &&Conditional(const bool x, Lhs &&lhs, Rhs &&rhs) {
if (x)
return std::forward<Lhs>(lhs);
return std::forward<Rhs>(rhs);
}

int main(int argc, char* argv) {
const bool (&t)[3] = Conditional(true, obj.a, obj.a);
return 0;
}


PS: Conditional isn't a constexpr function.



Or: const bool (&t)[3] = *(true ? &obj.a : &obj.a);







share|improve this answer














share|improve this answer



share|improve this answer








edited Nov 23 '18 at 12:56

























answered Nov 23 '18 at 12:38









felixfelix

1,473314




1,473314













  • Thanks your solution to reference on ternary and dereference the result do the job for me

    – Gurdil
    Nov 23 '18 at 13:01



















  • Thanks your solution to reference on ternary and dereference the result do the job for me

    – Gurdil
    Nov 23 '18 at 13:01

















Thanks your solution to reference on ternary and dereference the result do the job for me

– Gurdil
Nov 23 '18 at 13:01





Thanks your solution to reference on ternary and dereference the result do the job for me

– Gurdil
Nov 23 '18 at 13:01


















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