We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.
dear all, i defind a struct in a head file and other file will be use this struct , i use keyword extern but always has warning or error message , please tell me really method. thanks a lot.
main.c ---------------- typedef union{ unsigned char Byte; struct{ unsigned _40:1; //Cmd 0 unsigned _41:1; //Acmd 41 unsigned _50:1; //Cmd 16 unsigned _49:1; //Cmd 9 unsigned b4:1; unsigned b5:1; unsigned b6:1; unsigned b7:1; }Audio; struct{ unsigned _51:1; //Cmd 17 read_single_block unsigned _58:1; //Cmd 24 write_single_block unsigned xx1:1; //Cmd 16 unsigned xx2:1; //Cmd 9 unsigned xb4:1; unsigned xb5:1; unsigned xb6:1; unsigned xb7:1; }Bits; }_Data; _Data init_flag; other.c ---------------------------------- extern struct _Data init_flag;
my_struct.h ------------------ typedef union{ unsigned char Byte; struct{ unsigned _40:1; //Cmd 0 unsigned _41:1; //Acmd 41 unsigned _50:1; //Cmd 16 unsigned _49:1; //Cmd 9 unsigned b4:1; unsigned b5:1; unsigned b6:1; unsigned b7:1; }Audio; struct{ unsigned _51:1; //Cmd 17 read_single_block unsigned _58:1; //Cmd 24 write_single_block unsigned xx1:1; //Cmd 16 unsigned xx2:1; //Cmd 9 unsigned xb4:1; unsigned xb5:1; unsigned xb6:1; unsigned xb7:1; }Bits; }_Data; extern _Data init_flag; main.c ---------------- #include "my_struct.h" ..... ..... init_flag.Audio._40=1; ........... *** WARNING L1: UNRESOLVED EXTERNAL SYMBOL *** WARNING L2: REFERENCE MADE TO UNRESOLVED EXTERNAL
In _one_ of your source files, add a line:
_Data init_flag;
The "extern" lines only informs the compiler that somewhere there is a variable init_flag. You must follow up by actually allocating the variable somewhere too.
thanks a lot . i extern the struct success.