对构造函数的调用不能出现在常量表达式中

Question

While I run make build for the project DeSiNe , I am getting the error: a call to a constructor cannot appear in a constant-expression

$ make build
mkdir -m 755 -p obj/Algorithm
g++ -Wall -DNO_TIMER -DNO_TRACES  -O3 -funroll-loops -finline-functions -fexpensive-optimizations -Isrc -o obj/Algorithm/Algorithm.o -c src/Algorithm/Algorithm.cpp
src/Network/Link.h:44:42: error: a call to a constructor cannot appear in a constant-expression
     static const double METRIC_MIN = 1.0/DBL_MAX; // to prevent metric to be 0
                                          ^
src/Network/Link.h:45:38: error: a call to a constructor cannot appear in a constant-expression
     static const double METRIC_MAX = DBL_MAX;
                                      ^

As per Call to a constructor cannot appear in a constant-expression if I change the code in side the Link class definition in Network\\Link.h from

static const double METRIC_MIN = 1.0/DBL_MAX; // to prevent metric to be 0
static const double METRIC_MAX = DBL_MAX;

to

static const double METRIC_MIN; // to prevent metric to be 0
double METRIC_MIN = 1.0/DBL_MAX;
static const double METRIC_MAX;
double METRIC_MAX = DBL_MAX;

I receive

error: ‘double Link::METRIC_MIN’ conflicts with a previous declaration
double METRIC_MIN = 1.0/DBL_MAX;

Answer 1

Added in Link.cpp [See DeSiNe link above for full code please]

double METRIC_MIN = 1.0/DBL_MAX;
double METRIC_MAX = DBL_MAX;

as suggested by @immibis

Answer 2

The other SO question's answer that you linked to was unclear about where to write the lines. I have edited it so hopefully nobody else is misled.

To fix the compilation errors in C++03, change:

static const double METRIC_MIN = 1.0/DBL_MAX; // to prevent metric to be 0
static const double METRIC_MAX = DBL_MAX;

to:

static const double METRIC_MIN; // to prevent metric to be 0
static const double METRIC_MAX;

and then in exactly one .cpp file (it doesn't matter which, so long as Link.h is included by that file) add the following lines at file scope:

const double Link::METRIC_MIN = 1.0/DBL_MAX;
const double Link::METRIC_MAX = DBL_MAX;

---

However there may be further issues. Clearly whoever wrote this code was using a compiler with an extension that treated DBL_MAX as a constant expression prior to C++11. It's possible that the rest of the code relies on the value of these constants being visible in the header.

If you fix this bug then get compilation errors from other parts of the code relating to these variables then you may have to try a different solution (which will involve more code editing).

Answer 3

#define METRIC_MIN DBL_MIN
#define METRIC_MAX DBL_MAX

seems to work well