解决编译warning：warning: ‘MeteringUnit::voltage_gain_’ will be initialized after [-Wreorder]

问题：

环境：ubuntu 12.04，g++版本4.6.3，编译目标文件时出现warnings：

u1204@u1204-zhw:~/hwsvn/2sw/4prj_mips/UCP_rt5350/src/trunk$ make clean;make
rm -f *.o local_ctrl
g++ -g3 -Wall -o0 -c msgrcv_cmd.cpp -o msgrcv_cmd.o
In file included from msgrcv_cmd.h:24:0,
                 from msgrcv_cmd.cpp:30:
controller.h: In constructor ‘MeteringUnit::MeteringUnit(size_t, double, double, double)’:
controller.h:92:12: warning: ‘MeteringUnit::voltage_gain_’ will be initialized after [-Wreorder]
controller.h:91:12: warning:   ‘double MeteringUnit::current_gain_’ [-Wreorder]
controller.h:77:5: warning:   when initialized here [-Wreorder]
g++ -g3 -Wall -o0 -c controller.cpp -o controller.o
In file included from controller.cpp:21:0:
controller.h: In constructor ‘MeteringUnit::MeteringUnit(size_t, double, double, double)’:
controller.h:92:12: warning: ‘MeteringUnit::voltage_gain_’ will be initialized after [-Wreorder]
controller.h:91:12: warning:   ‘double MeteringUnit::current_gain_’ [-Wreorder]
controller.h:77:5: warning:   when initialized here [-Wreorder]
g++ -g3 -Wall -o0 -c thread.cpp -o thread.o
g++ -g3 -Wall -o0 -c ini_file.cpp -o ini_file.o
g++ -g3 -Wall -o0 -c main_ctrl.cpp -o main_ctrl.o
In file included from main_ctrl.cpp:25:0:
controller.h: In constructor ‘MeteringUnit::MeteringUnit(size_t, double, double, double)’:
controller.h:92:12: warning: ‘MeteringUnit::voltage_gain_’ will be initialized after [-Wreorder]
controller.h:91:12: warning:   ‘double MeteringUnit::current_gain_’ [-Wreorder]
controller.h:77:5: warning:   when initialized here [-Wreorder]

解决办法：

1. 出问题的地方在头文件controller.h中，

class MeteringUnit {
public:
    MeteringUnit(size_t port_num = 1, double pgain = 1.0, double cgain = 1.0, double vgain = 1.0)
    : port_(port_num), power_gain_(pgain), voltage_gain_(vgain), current_gain_(cgain) { }
    ~MeteringUnit();
    void Refresh();
    double Power() const;
    double Current() const;
    double Voltage() const;
private:
    size_t port_;
    operation* mu_op_;
    static const SensorType sensor_typ_ = EMETER;
private:
    static const int emeter_pulse_const_ = 3200;
    double power_gain_;
    double current_gain_;
    double voltage_gain_;
    double power_;
    double current_;
    double voltage_;
	int gpqs1_;	// GP1/GQ1/GS1(0x50/0x51/0x52)
	int gphs1_;	// Gphs1(0x6d)
	int p1offset_;	// P1offset(0x65)
};

从编译后的提示，已经可以很明白地看出错在什么地方了，
MeteringUnit::voltage_gain_应该在double MeteringUnit::current_gain_之后初始化。

也就是说，构造函数中变量初始化的顺序与该成员变量在类MeteringUnit中定义的顺序不一致。

将其中的两行

    MeteringUnit(size_t port_num = 1, double pgain = 1.0, double cgain = 1.0, double vgain = 1.0)
    : port_(port_num), power_gain_(pgain), voltage_gain_(vgain), current_gain_(cgain) { }

改为

    MeteringUnit(size_t port_num = 1, double pgain = 1.0, double cgain = 1.0, double vgain = 1.0)
    : port_(port_num), power_gain_(pgain), current_gain_(cgain), voltage_gain_(vgain) { }

重新编译，问题解决。

u1204@u1204-zhw:~/hwsvn/2sw/4prj_mips/UCP_rt5350/src/trunk$ make clean;make
rm -f *.o local_ctrl
g++ -g3 -Wall -o0 -c msgrcv_cmd.cpp -o msgrcv_cmd.o
g++ -g3 -Wall -o0 -c controller.cpp -o controller.o
g++ -g3 -Wall -o0 -c thread.cpp -o thread.o
g++ -g3 -Wall -o0 -c ini_file.cpp -o ini_file.o
g++ -g3 -Wall -o0 -c main_ctrl.cpp -o main_ctrl.o
g++ -o local_ctrl msgrcv_cmd.o controller.o thread.o ini_file.o main_ctrl.o -L../../drivers -lphysicalop -lpthread