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colt
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Joined: 17 Apr 2018
Posts: 17
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 Posted: Tue Feb 13, 2024 1:25 pm Post subject: Initializer list complains about number of arguments. |
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Hi. I have a structure that I initialize through this code:
| Code: | | Sphere sphere2 {{300,240,-300},40000,1}; |
which cause the following error messages:
| Code: | raytracer.cpp: In function ‘int main()’:
raytracer.cpp:256:39: error: no matching function for call to ‘Sphere::Sphere(<brace-enclosed initializer list>)’
Sphere sphere {{300,240,-100},10000,1};
^
raytracer.cpp:256:39: note: candidates are:
raytracer.cpp:217:8: note: constexpr Sphere::Sphere(const Sphere&)
struct Sphere {
^
raytracer.cpp:217:8: note: candidate expects 1 argument, 3 provided
raytracer.cpp:217:8: note: constexpr Sphere::Sphere(Sphere&&)
raytracer.cpp:217:8: note: candidate expects 1 argument, 3 provided
raytracer.cpp:257:40: error: no matching function for call to ‘Sphere::Sphere(<brace-enclosed initializer list>)’
Sphere sphere2 {{300,240,-300},40000,1};
^
raytracer.cpp:257:40: note: candidates are:
raytracer.cpp:217:8: note: constexpr Sphere::Sphere(const Sphere&)
struct Sphere {
^
raytracer.cpp:217:8: note: candidate expects 1 argument, 3 provided
raytracer.cpp:217:8: note: constexpr Sphere::Sphere(Sphere&&)
raytracer.cpp:217:8: note: candidate expects 1 argument, 3 provided |
So I want to understand what's happening, like why it's expecting only one argument, and also why these error messages just vanishes when I comment out the "private" modifier for the variables to be initialized. |
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GDH-gentoo
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Joined: 20 Jul 2019
Posts: 1949
Location: South America
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| Posted: Tue Feb 13, 2024 1:55 pm Post subject: |
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How is class Sphere defined in that program? I'm assuming from context that it is a C++ program.
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| NeddySeagoon wrote: | I'm not a witch, I'm a retired electronics engineer  |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
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logrusx
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Joined: 22 Feb 2018
Posts: 3152
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| Posted: Tue Feb 13, 2024 3:07 pm Post subject: Re: Initializer list complains about number of arguments. |
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| colt wrote: | Hi. I have a structure that I initialize through this code:
| Code: | | Sphere sphere2 {{300,240,-300},40000,1}; |
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That looks like a recursive definition, something like struct Sphere {Sphere, int, int} but when you pass the structure for the first argument, you pass three ints while it asks for a sphere and two ints. My C is very rusty, but I think the only way that could work is if the first argument in the inner parentheses is 0 or NULL. Or a valid Sphere initializer, but then at some depth you need to pass 0 or NULL.
Best Regards,
Georgi |
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GDH-gentoo
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Joined: 20 Jul 2019
Posts: 1949
Location: South America
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| Posted: Tue Feb 13, 2024 3:11 pm Post subject: |
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Based on the comment about the private member(s), the OP is probably trying to use aggregate initialization (i. e. C structure intialization-style syntax) for a C++ class that isn't an aggregate, but without the class definition, we are just guessing.
_________________
| NeddySeagoon wrote: | | I'm not a witch, I'm a retired electronics engineer |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
Last edited by GDH-gentoo on Tue Feb 13, 2024 5:04 pm; edited 1 time in total |
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logrusx
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Joined: 22 Feb 2018
Posts: 3152
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| Posted: Tue Feb 13, 2024 3:36 pm Post subject: |
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It looks like a C inline structure initialization to me, but again, my C is a good 20 y.o. if not more... And my C++ was worse than my C was at that time, so yes - a wild guesswork from my side.
Best Regards,
Georgi |
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Hu
Administrator
Joined: 06 Mar 2007
Posts: 23671
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| Posted: Tue Feb 13, 2024 4:12 pm Post subject: |
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| colt wrote: | | So I want to understand what's happening, like why it's expecting only one argument, |
It considered all the standard constructors (copy, move), which by definition take only one argument. Which constructor did you expect to use? | colt wrote: | | and also why these error messages just vanishes when I comment out the "private" modifier for the variables to be initialized. |
Is the structure eligible to be an aggregate, when its members are public?
That double-level brace can work, depending on the definition of the structure. This works in C++20 mode: | Code: | #include <array>
struct Sphere
{
std::array<int, 3> a;
int b;
int c;
};
void x()
{
Sphere sphere2 {{300,240,-300},40000,1};
(void)sphere2;
} |
The inner braced expression becomes the initializer for a.
OP: if you need help, please follow the stackoverflow advice: provide a minimal program, and the compiler invocation to use it, that will exhibit your problem. |
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sam_
Developer
Joined: 14 Aug 2020
Posts: 2400
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| Posted: Tue Feb 13, 2024 7:07 pm Post subject: |
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| In C, you can and should use designated initialisers. You don't (surprisingly!) have that option in C++ until C++20. |
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colt
n00b
Joined: 17 Apr 2018
Posts: 17
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| Posted: Wed Feb 14, 2024 9:59 pm Post subject: |
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Here is the class (struct) definition that shall answer all the doubts, I think
| Code: | struct Sphere {
public:
bool intersect (Vec3f origin, Vec3f dir, float t) {};
int getColor () {return color;}
//Vec3f getCenter () {return center;}
private:
Vec3f center;
float radius_squared;
int color;
};' |
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GDH-gentoo
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Joined: 20 Jul 2019
Posts: 1949
Location: South America
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| Posted: Wed Feb 14, 2024 11:05 pm Post subject: |
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I see. This kind of initialization:
| colt wrote: | | Code: | | Sphere sphere2 {{300,240,-300},40000,1}; |
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i. e., providing a list of initializers that correspond to class members in declaration order, is one form of what is called aggregate initialization. Which, in C++, can be used only for classes that are aggregates. There's a list of conditions that make a class an aggregate, but having private members makes a class not an aggregate. Therefore, your code fails [1]. If you want to initialize an object of such a class in the way that you thought that would work, you need to write a constructor, such as:
| Code: | struct Sphere {
private:
Vec3f center;
float radius_squared;
int color;
public:
bool intersect (Vec3f origin, Vec3f dir, float t) {
/* I suppose there's actually code here, otherwise
calling this has undefined behaviour */
}
int getColor () {return color;}
//Vec3f getCenter () {return center;}
Sphere (float x, float y, float z, float r2, int c):
center{x, y, z}, radius_squared(r2), color(c) {}
}; |
And, with this definition, then do:
| Code: | | Sphere sphere2(300,240,-300,40000,1); |
That works if an object of type Vec3f can in turn be initialized with an initializer list containing 3 float elements, which may or may not be possible in your program, depending on the definition of class Vec3f.
[1] It is possible to initialize an object of a class that is not an aggregate with a braced initializer list, but that calls a constructor instead, which is what the compiler tried to generate code for and failed, because there was no suitable constructor.
_________________
| NeddySeagoon wrote: | | I'm not a witch, I'm a retired electronics engineer |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
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