C programming Dereferencing pointer to incomplete type error

Question

I have a struct defined as     struct    char name 32    int  size   int  start   int  popularity    stasher file    and an array of pointers to those structs     struct stasher file  files TOTAL STORAGE SIZE     In my code  I m making a pointer to the struct and setting its members  and adding it to the array         struct stasher file  newFile   strncpy newFile- gt name  name  32    newFile- gt size   size   newFile- gt start   first free   newFile- gt popularity   0   files num files    newFile         I m getting the following error      error  dereferencing pointer to incomplete type   whenever I try to access the members inside newFile  What am I doing wrong

User · Answer

The reason why you re getting that error is because you ve declared your struct as   struct    char name 32    int  size   int  start   int  popularity    stasher file    This is not declaring a stasher file type   This is declaring an anonymous struct type and is creating a global instance named stasher file   What you intended was   struct stasher file    char name 32    int  size   int  start   int  popularity       But note that while Brian R  Bondy s response wasn t correct about your error message  he s right that you re trying to write into the struct without having allocated space for it   If you want an array of pointers to struct stasher file structures  you ll need to call malloc to allocate space for each one   struct stasher file  newFile   malloc sizeof  newFile   if  newFile    NULL          Failure handling goes here       strncpy newFile- gt name  name  32   newFile- gt size   size         BTW  be careful when using strncpy  it s not guaranteed to NUL-terminate

User · Answer

You haven t defined struct stasher file by your first definition  What you have defined is an nameless struct type and a variable stasher file of that type  Since there s no definition for such type as struct stasher file in your code  the compiler complains about incomplete type   In order to define struct stasher file  you should have done it as follows  struct stasher file    char name 32    int  size   int  start   int  popularity       Note where the stasher file name is placed in the definition

User · Answer

How did you actually define the structure  If   struct     char name 32     int  size    int  start    int  popularity    stasher file    is to be taken as type definition  it s missing a typedef  When written as above  you actually define a variable called stasher file  whose type is some anonymous struct type   Try  typedef struct         stasher file     or  as already mentioned by others    struct stasher file            The latter actually matches your use of the type  The first form would require that you remove the struct before variable declarations

User · Answer

You are using the pointer newFile without allocating space for it    struct stasher file  newFile   malloc sizeof stasher file      Also you should put the struct name at the top   Where you specified stasher file is to create an instance of that struct   struct stasher file       char name 32       int  size      int  start      int  popularity

User · Answer

the case above is for a new project   I hit upon this error while editing a fork of a well established library   the typedef was included in the file I was editing but the struct wasn t      The end result being that I was attempting to edit the struct in the wrong place   If you run into this in a similar way look for other places where the struct is edited and try it there

[c] C programming: Dereferencing pointer to incomplete type error

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