initialize an array of structs with function pointers in them C

Question

I am trying to initialize an array of structs. the structs have function pointers in them and are defined as such:

typedef struct{
      char str[512];
      char *fptr;
} infosection;

then I try to make an array:

infosection section[] = {
      ("Software", *SoftwarePtr),
      ("Hardware", *HardwarePtr),
 }

I defined the function pointers using a simple tutorial. Function Software returns an int

int (*SoftwarePtr)()=NULL;
SoftwarePtr = &Software;

My question is about the warnings I get upon compiling.

Initialization makes integer from pointer without a cast

The warning references the lines in the section array.

So I have two doubts:

Am I misusing the */&/neither for the pointer?I have tried combinations of each and i still seem to get the same warning.I am aware of the meaning of each, just unsure how they apply in this particular instance.
Can I declare an instance of the infosection struct in an array as i do here?I have seen many examples where people declare their array of struct in a for loop, However my final product requires a long list of structs to be contained in that array.I would like to make my code portable such that people can add structs ( strings which correspond with functions to point to) in an easy list-like fashion as seen about. Is this the only way to declare an instance of the array
```
  infosection section[];
  section[0].str="software";
  section[0].fptr=SoftwarePtr;
```

Just to clarify, i have done quite a bit of research on structs, array of structs, and function pointers. It just seems that the combination of the 3 is causing trouble.

@Jim I read here: newty.de/fpt/fpt.html#defi that function pointer's need to be declared with the return type of the function they point to... — umphish
– umphish, Commented Jul 26, 2013 at 18:00
char *fptr; This is not a function pointer and conversions between char* and a function pointer are not well-defined — Lundin
– Lundin, Commented May 26, 2015 at 14:45
Anyway, a better question might be: which crap compiler allowed all of these errors to slip through? Please don't tell me you are using Turbo C... — Lundin
– Lundin, Commented May 26, 2015 at 14:51

Grijesh Chauhan · Accepted Answer · 2015-06-27 13:51:12Z

7

One

One mistake I an find, in structure declaration of function pointer is incorrect:

typedef struct{
      char str[512];
      int (*fptr)();  // not char* fptr
} infosection;

Two

declaration:

infosection section[] = {
      ("Software", *SoftwarePtr),
      ("Hardware", *HardwarePtr),
 }

Should be:

infosection section[] = {
      {"Software", SoftwarePtr},
      {"Hardware", HardwarePtr}
 }

Remove *. and replace inner ( ) with { }.

three:

infosection section[];
section[0].str="software"; // compiler error
section[0].fptr=SoftwarePtr;

Is wrong you can't assign string in this way. you need to use strcpy() as follows;

strcpy(section[0].str, "software");

edited Jun 27, 2015 at 13:51

answered Jul 26, 2013 at 17:58

Grijesh Chauhan

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1 Comment

Lundin Over a year ago

There is nothing wrong with the trailing comma: some coding styles even favour it as it makes each row consistent. Array initialization lists have always allowed to have trailing commas on the last row.

krs · Accepted Answer · 2013-07-26 18:00:01Z

2

The struct member is currently a char*, change to the correct pointer type for your function signature.

typedef struct{
  char str[512];
  int (*fptr)();
} infosection;

* dereference the pointer, read *foo as "what foo points at". You want to set the struct member to the actual pointer, also use bracets instead of paranthesis.

infosection section[] = {
  {"Software", SoftwarePtr},
  {"Hardware", HardwarePtr}
}

answered Jul 26, 2013 at 18:00

krs

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Comments

Mr.Monshaw · Accepted Answer · 2013-07-26 21:42:50Z

1

been a while since i was playin around with pointers but maybe a constructor would help?

struct infosection{
      char str[512];
      char *fptr;
      infosection(char* strN, char* fptrN): str(strN), fptr(fptrN) {}
};

infosection[] isxn = { new infosection(&str1,fptr1), 
               new infosection(&str2,fptr2)},
               ... };

my apologies...where c stops and c++ begins has become blurred in my mind, i have seen a workaround for c that looks like this (but not exactly, im sure some of the pointer stuff is mixed up but this was the idea)

struct infosection{
  char str[512];
  char *fptr;
};

infosection* myIS (char *strN, char *fptrN) {
  infosection i = new infosection();
  i.str = &strN;
  i.fptr = fptrN;
  return *i;
}

//infosection* newInfoSection = myIS(myStrPtr,myFptr);

edited Jul 26, 2013 at 21:42

answered Jul 26, 2013 at 18:26

Mr.Monshaw

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1 Comment

krs Over a year ago

Constuctors are a part of C++ though, and wont work in this senario =)

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