嵌入式 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