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：

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1. u1204@u1204-zhw:~/hwsvn/2sw/4prj_mips/UCP_rt5350/src/trunk$ make clean;make  
2. rm -f *.o local_ctrl  
3. g++ -g3 -Wall -o0 -c msgrcv_cmd.cpp -o msgrcv_cmd.o  
4. In file included from msgrcv_cmd.h:24:0,  
5.                  from msgrcv_cmd.cpp:30:  
6. controller.h: In constructor ‘MeteringUnit::MeteringUnit(size_t, double, double, double)’:  
7. controller.h:92:12: warning: ‘MeteringUnit::voltage_gain_’ will be initialized after [-Wreorder]  
8. controller.h:91:12: warning:   ‘double MeteringUnit::current_gain_’ [-Wreorder]  
9. controller.h:77:5: warning:   when initialized here [-Wreorder]  
10. g++ -g3 -Wall -o0 -c controller.cpp -o controller.o  
11. In file included from controller.cpp:21:0:  
12. controller.h: In constructor ‘MeteringUnit::MeteringUnit(size_t, double, double, double)’:  
13. controller.h:92:12: warning: ‘MeteringUnit::voltage_gain_’ will be initialized after [-Wreorder]  
14. controller.h:91:12: warning:   ‘double MeteringUnit::current_gain_’ [-Wreorder]  
15. controller.h:77:5: warning:   when initialized here [-Wreorder]  
16. g++ -g3 -Wall -o0 -c thread.cpp -o thread.o  
17. g++ -g3 -Wall -o0 -c ini_file.cpp -o ini_file.o  
18. g++ -g3 -Wall -o0 -c main_ctrl.cpp -o main_ctrl.o  
19. In file included from main_ctrl.cpp:25:0:  
20. controller.h: In constructor ‘MeteringUnit::MeteringUnit(size_t, double, double, double)’:  
21. controller.h:92:12: warning: ‘MeteringUnit::voltage_gain_’ will be initialized after [-Wreorder]  
22. controller.h:91:12: warning:   ‘double MeteringUnit::current_gain_’ [-Wreorder]  
23. 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，

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1. class MeteringUnit {  
2. public:  
3.     MeteringUnit(size_t port_num = 1, double pgain = 1.0, double cgain = 1.0, double vgain = 1.0)  
4.     : port_(port_num), power_gain_(pgain), voltage_gain_(vgain), current_gain_(cgain) { }  
5.     ~MeteringUnit();  
6.     void Refresh();  
7.     double Power() const;  
8.     double Current() const;  
9.     double Voltage() const;  
10. private:  
11.     size_t port_;  
12.     operation* mu_op_;  
13.     static const SensorType sensor_typ_ = EMETER;  
14. private:  
15.     static const int emeter_pulse_const_ = 3200;  
16.     double power_gain_;  
17.     double current_gain_;  
18.     double voltage_gain_;  
19.     double power_;  
20.     double current_;  
21.     double voltage_;  
22.     int gpqs1_; // GP1/GQ1/GS1(0x50/0x51/0x52)  
23.     int gphs1_; // Gphs1(0x6d)  
24.     int p1offset_;  // P1offset(0x65)  
25. };  

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

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

改为

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

重新编译，问题解决。

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