Copy struct to struct in C

Question

I want to copy an identical struct into another and later on use it as a comparance to the first one  The thing is that my compiler gives me a warning when Im doing like this  Should I do it in another way or am I doing this wrong   In header File   extern struct RTCclk   uint8 t second  uint8 t minute  uint8 t hour  uint8 t mday  uint8 t month  uint8 t year    RTCclk    In C file   struct RTCclk RTCclk  struct RTCclk RTCclkBuffert   void FunctionDO void              Some Code       Copy first struct values into the second one       memcpy  amp RTCclk   amp RTCclkBuffert  sizeof RTCclk

User · Answer

I think you should cast the pointers to (void *) to get rid of the warnings.

memcpy((void *)&RTCclk, (void *)&RTCclkBuffert, sizeof RTCclk);

Also you have use sizeof without brackets, you can use this with variables but if RTCclk was defined as an array, sizeof of will return full size of the array. If you use use sizeof with type you should use with brackets.

sizeof(struct RTCclk)

User · Answer

copy structure in c you just need to assign the values as follow    struct RTCclk RTCclk1  struct RTCclk RTCclkBuffert   RTCclk1 second 3  RTCclk1 minute 4  RTCclk1 hour 5   RTCclkBuffert RTCclk1    now RTCclkBuffert hour will have value 5   RTCclkBuffert minute will have value 4  RTCclkBuffert second will have value 3

User · Answer

Also a good example        struct point int x y    typedef struct point point t  typedef struct       struct point ne se sw nw   rect t  rect t temp    int main       rotate     RotateRect  amp temp       return 0     void RotateRect rect t  givenRect        point t temp point        Copy struct data from struct to struct within a struct       temp point   givenRect- gt sw      givenRect- gt sw   givenRect- gt se      givenRect- gt se   givenRect- gt ne      givenRect- gt ne   givenRect- gt nw      givenRect- gt nw   temp point

User · Answer

For simple structures you can either use memcpy like you do  or just assign from one to the other   RTCclk   RTCclkBuffert    The compiler will create code to copy the structure for you     An important note about the copying  It s a shallow copy  just like with memcpy  That means if you have e g  a structure containing pointers  it s only the actual pointers that will be copied and not what they point to  so after the copy you will have two pointers pointing to the same memory

User · Answer

Your code is correct  You can also assign one directly to the other  see Joachim Pileborg s answer    When you later come to compare the two structs  you need to be careful to compare the structs the long way  one member at a time  instead of using memcmp  see How do you compare structs for equality in C

User · Answer

Your memcpy code is correct   My guess is you are lacking an include of string h  So the compiler assumes a wrong prototype of memcpy and thus the warning   Anyway  you should just assign the structs for the sake of simplicity  as Joachim Pileborg pointed out

User · Answer

memcpy expects the first two arguments to be void    Try  memcpy   void   amp RTCclk   void   amp RTCclkBuffert  sizeof RTCclk      P S  although not necessary  convention dictates the brackets for the sizeof operator   You can get away with a lot in C that leaves code impossible to maintain  so following convention is the mark of a good  employable  C programmer

[c] Copy struct to struct in C

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