Is it proper to initialize variables in a structure define in typedef (C programming)

Question

typedef struct
{
    int id = 0;
    char *name = NULL;
    char *department = NULL;
    int phone = 0;
} emp;

In C programming is it a good programming practice to do something like that, or, should I initialize when I declare the variable 'emp'.

I am using a GCC compiler and the above code does compile. I want to know if it is the proper way of initializing.

Which version of GCC are you using on which platform? It should not compile in any version. It does not compile with GCC 4.8.2 on Mac OS X 10.9.2 even with none of the strictures I normally use. I get the error `duff.c:3:12: error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘=’ token int id = 0;` — Jonathan Leffler, Feb 27 '14 at 04:26

score 6 · Accepted Answer · answered Feb 27 '14 at 04:15

With typedef struct { ... } emp; you are creating a new complex type called "emp". When you declare a variable of type "emp", that is where you typically initialize it.

I would go with:

typedef struct
{
  int id;
  char *name;
  char *department;
  int phone;
} emp;

emp myVar = { 
  /* id */ 0, 
  /* name */ NULL, 
  /* department */, NULL, 
  /* phone */ 0 
};

score 1 · Answer 2 · answered Feb 27 '14 at 04:14

1

Since the syntax you show won't compile in a C compiler — nor a C++ compiler, AFAIK — you don't have any choice in the matter. You can't do what you are trying to do and must initialize when you declare a variable of type emp.

answered Feb 27 '14 at 04:14

Jonathan Leffler

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@yogisha: See my comment to the question. Frankly, I don't believe you, but please provide the details of compiler version, platform where you're running it, and any options other than `-c` that you're using to get the source to compile. I took the code from the question and placed it into a file `duff.c` and tried to compile it. Even at its laxest, GCC 4.8.2 won't compile the code. – Jonathan Leffler Feb 27 '14 at 04:27
gcc version 4.1.2 20080704 (Red Hat 4.1.2-44) , I placed the code in a 'header.h' file and included the file in main.c, Used 'gcc -c main.c -I../include/' to compile – yogisha Feb 27 '14 at 04:30
I would hazard a guess that you're using a different `header.h`. I don't have a copy of GCC 4.1.2 any more; the oldest version I have on hand is 4.4.2…oh, unless I try that other VM…pause for reactivation (and upgrade, I expect) of the VM…a SuSE 10.5 VM has 'gcc (GCC) 4.1.2 20070115 (SUSE Linux)' and it generates the message: `duff.c:3: error: expected ‘:’, ‘,’, ‘;’, ‘}’ or ‘__attribute__’ before ‘=’ token`. Granted, not identical to your compiler, but very similar. – Jonathan Leffler Feb 27 '14 at 04:34
I'm not going to initialze like that anyways, thank you – yogisha Feb 27 '14 at 04:42
@yogisha: OK; you certainly aren't going to initialize as shown in the question. As a point of detail, I said 'SuSE 10.5 VM'; that's incorrect — it is SuSE 10SP2. It doesn't make very much difference. Good luck. Note that you can specify `-std=c99` and use designated initializers if you want: `static emp employee = { .id = 1, .name = "no-one", .department = "mythology", .phone = "999-888-7777" };`. You don't even have to have them in the correct order, though it is easiest if they are. – Jonathan Leffler Feb 27 '14 at 04:48
@JonathanLeffler The given code in the OP compiles even in MSVS 2017. I didn't know it was a bad practice (or basically a non valid one in C) because of this. – SarpSTA Mar 31 '18 at 19:23
@SarpSTA: ‘Tis interesting that it compiles in VS 2017. I think it would not have compiled in those available when the question was asked in 2014. – Jonathan Leffler Mar 31 '18 at 19:37
@JonathanLeffler I can't talk for 2014 but it compiles on 2015 version too. I don't know about the compiler MSVS uses but it probably is a C++ compiler. – SarpSTA Mar 31 '18 at 21:01

score 0 · Answer 3 · answered Feb 27 '14 at 04:10

0

Better to initialize when you declare emp

answered Feb 27 '14 at 04:10

user376507

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score 0 · Answer 4 · answered Feb 27 '14 at 04:20

In plain C, you can't give default values to struct members. If it's useful to create it with some default values, you could write a function like this:

void emp_set_defaults(emp *e)
{
    assert(e != NULL);
    e->id = 0;
    e->name = NULL;
    e->department = NULL;
    e->phone = 0;
}

and use it like

emp e;
emp_set_defaults(&e);

score 0 · Answer 5 · edited May 23 '17 at 12:34

0

In C99 you can use designated initializers to create a struct object with its members filled in by name. Here's an example:

emp myVar = { 
  .id = 0, 
  .name = NULL, 
  .department = NULL, 
  .phone = 0 
};

More info at C struct initialization using labels. It works, but how? Documentation?

edited May 23 '17 at 12:34

Community

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answered Feb 27 '14 at 04:50

StilesCrisis

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Is it proper to initialize variables in a structure define in typedef (C programming)

5 Answers5