GDB incomplete type forward enum : int declaration

Question

I use a forward enum declaration in my cpp program that is causing gdb to give me an incompatible type. Here is a minimal working example:

definitions.h:

/*definitions.h*/
#ifndef DEFINITIONS_H_
#define DEFINITIONS_H_

enum ForwardEnum : int;
typedef ForwardEnum ForwardEnum;

typedef struct {
const ForwardEnum EnumValue;
} ElemConfig;

#endif //DEFINITIONS_H_

config.h:

/*config.h*/
#ifndef CONFIG_H_
#define CONFIG_H_

#include "definitions.h"

enum ForwardEnum : int {
    EnumValue1 = -1,
    EnumValue2,
};

#endif //CONFIG_H_

classA.h:

/*classA.h*/
#ifndef CLASSA_H_
#define CLASSA_H_

#include <array>
#include "definitions.h"
#define N_ELEMS 8

class A{
    private:
        const std::array<ElemConfig, N_ELEMS> Config;
    public:
        A(const std::array<ElemConfig, N_ELEMS>);
 };

#endif //CLASSA_H_

main.cpp:

/*main.cpp*/
#include <iostream>
#include <array>
#include "definitions.h"
#include "config.h"
#include "classA.h"

const std::array<ElemConfig, N_ELEMS> AConfig {{{EnumValue1}}};

A::A(const std::array<ElemConfig, N_ELEMS> Config) : Config(Config) 
{
    ForwardEnum a = Config[0].EnumValue;
    std::cout << a << std::endl;
};

int main(void)
{
    A objectA(AConfig);
}

When I try to debug the class A constructor in gdb I get an incomplete type for the enum variable. According to this question I tried casting it to what I think is the compatible type:

print (ForwardEnum) a

When that failed I experimented to see if the problem was the typedef:

print (const enum ForwardEnum) a

And also to disassemble the constructor, but it all failed.

What is then the correct type conversion to print the content of EnumValue?

(Or, alternatively, How can I get gdb to resolve the incompatible type, while keeping the forward declaration?)

I am using gdb 7.7.1 and gcc 4.8.4

@VTT to have the system configuration (which includes the possible enum values) in a separate file. The configuration structure needs then to store the enum value — calofr, Jun 05 '18 at 11:02
But how does that `typedef` help? `typedef` for `struct` seems to be useless as well. — user7860670, Jun 05 '18 at 11:03
In my real applicaiton I sometimes use ForwardEnum auxiliary variables, so it saves some writting. — calofr, Jun 05 '18 at 11:21
How could it save some writing if type alias name has exactly the same length? — user7860670, Jun 05 '18 at 11:22

score 1 · Answer 1 · edited Aug 17 '20 at 09:50

1

Try using print /d a. /d means format as an integer.

See help x and help print in gdb.

edited Aug 17 '20 at 09:50

Jan Schultke

17,446
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answered Aug 17 '20 at 09:06

jqknono

84
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GDB incomplete type forward enum : int declaration

1 Answers1