How do you make an array of structs in C

Question

I m trying to make an array of structs where each struct represents a celestial body   I don t have that much experience with structs  which is why I decided to try to use them instead of a whole bunch of arrays  However  I keep on running into numerous different errors  I ve tried to implement the techniques that I ve seen on various threads and on StackOverflow  such as Array of structs in C and C - initialize array of structs   however not all of them were applicable   Further information for those who have read this far  I don t need any of this to be dynamic  I know define the size of everything beforehand   I also need this to be a global array as I m accessing this in several different methods which have defined arguments  i e  GLUT methods      This is how I m defining the struct in my header   struct body       double p 3    position     double v 3    velocity     double a 3    acceleration     double radius      double mass       I have a list of other global variables that I m defining before I define the interior of the struct  and one of those is the array of this struct  basically  if I m being too unclear in my fogged speak  the line below is above the stuff above    struct body bodies n     Just so you know  n is something that I ve legitimately defined  i e   define n 1      I use this array in several different methods  but the easiest and least space consuming one is a simplified form of my main  Here I initialize all of the variables in each of the structs  just to set the variables for certain before I modify them in some way     int a  b   for a   0  a  lt  n  a               for b   0  b  lt  3  b                          bodies a  p b    0              bodies a  v b    0              bodies a  a b    0                    bodies a  mass   0          bodies a  radius   1 0       The current error that I m facing is nbody c 32 13  error  array type has incomplete element type where line 32 is where I m making the array of the structs   One last clarification  by header I mean the space above int main void  but in the same   c file

User · Answer

Another way of initializing an array of structs is to initialize the array members explicitly. This approach is useful and simple if there aren't too many struct and array members.

Use the typedef specifier to avoid re-using the struct statement everytime you declare a struct variable:

typedef struct
{
    double p[3];//position
    double v[3];//velocity
    double a[3];//acceleration
    double radius;
    double mass;
}Body;

Then declare your array of structs. Initialization of each element goes along with the declaration:

Body bodies[n] = {{{0,0,0}, {0,0,0}, {0,0,0}, 0, 1.0}, 
                  {{0,0,0}, {0,0,0}, {0,0,0}, 0, 1.0}, 
                  {{0,0,0}, {0,0,0}, {0,0,0}, 0, 1.0}};

To repeat, this is a rather simple and straightforward solution if you don't have too many array elements and large struct members and if you, as you stated, are not interested in a more dynamic approach. This approach can also be useful if the struct members are initialized with named enum-variables (and not just numbers like the example above) whereby it gives the code-reader a better overview of the purpose and function of a structure and its members in certain applications.

User · Answer

move   struct body bodies n     to after   struct body       double p 3    position     double v 3    velocity     double a 3    acceleration     double radius      double mass       Rest all looks fine

User · Answer

That error means that the compiler is not able to find the definition of the type of your struct before the declaration of the array of structs  since you re saying you have the definition of the struct in a header file and the error is in nbody c then you should check if you re including correctly the header file  Check your  include s and make sure the definition of the struct is done before declaring any variable of that type

User · Answer

include lt stdio h gt   define n 3 struct body       double p 3    position     double v 3    velocity     double a 3    acceleration     double radius      double mass      struct body bodies n    int main         int a  b       for a   0  a  lt  n  a                       for b   0  b  lt  3  b                                  bodies a  p b    0                  bodies a  v b    0                  bodies a  a b    0                            bodies a  mass   0              bodies a  radius   1 0              return 0      this works fine  your question was not very clear by the way  so match the layout of your source code with the above

User · Answer

Solution using pointers    include lt stdio h gt   include lt stdlib h gt   define n 3 struct body       double p 3    position     double v 3    velocity     double a 3    acceleration     double radius      double  mass       int main         struct body  bodies    struct body  malloc n sizeof struct body        int a  b       for a   0  a  lt  n  a                       for b   0  b  lt  3  b                                  bodies a  p b    0                  bodies a  v b    0                  bodies a  a b    0                            bodies a  mass   0              bodies a  radius   1 0              return 0

User · Answer

I think you could write it that way too  I am also a student so I understand your struggle  A bit late response but ok     include lt stdio h gt   define n 3  struct       double p 3    position     double v 3    velocity     double a 3    acceleration     double radius      double mass   bodies n

User · Answer

So to put it all together by using malloc     int main int argc  char   argv        typedef struct          char  firstName          char  lastName          int day          int month          int year        STUDENT       int numStudents 3      int x      STUDENT  students   malloc numStudents   sizeof  students       for  x   0  x  lt  numStudents  x             students x  firstName  char  malloc sizeof char             scanf   s  students x  firstName           students x  lastName  char  malloc sizeof char             scanf   s  students x  lastName           scanf   d   amp students x  day           scanf   d   amp students x  month           scanf   d   amp students x  year              for  x   0  x  lt  numStudents  x            printf  first name   s  surname   s  day   d  month   d  year   d n  students x  firstName students x  lastName students x  day students x  month students x  year        return  EXIT SUCCESS

[c] How do you make an array of structs in C?

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