CODEWITHSUNDEEP
cmacros
iuradz
iuradz

Reputation: 1168

How can I perform looped macro in C

I have some macros defined such as

#define NUM_A 3
#define A1 10
#define A2 100
#define A3 8

The total count and the values are specific to the device. Now I need an array looks like

int Array[NUM_A]={A1, A2, A3};

Now, if the total number, NUM_A changes to 4, and I have defined the macro A4, but I forget to append A4 to the array. The actual Array would be {A1, A2, A3, 0}. There won't be error when compiling. The error is also hard to be found when running the program. It's more likely to be happen when I write the macros in the header file and declare the array in a source file. Can I write a looped macro to generate the array by the defined macros NUM_A, A1, A2 and A3? Or can I write an assert or something else to warn myself if the error occurs when compiling or running?

Upvotes: 0

Views: 128

Answers (3)

ryyker
ryyker

Reputation: 23218

In addition to declaring your variable with open array operators as A.M.D. has shown: 

  int arr[] = {A1, A2, A3};

You can also define a shorter representation of sizeof arr/sizeof arr[0], by defining a macro to replace that statement anywhere in your code where arr is defined like this: 

#define ARR_SIZE sizeof arr/sizeof arr[0]

The macro will evaluate to the number of array elements at run-time, And accommodates changes to number of elements in the array between run-times, with no need to edit the macro.

For arr[] = {1,2,5,8,9,3}; ARR_SIZE will evaluate to 6
For arr[] = {1,2,5,8,9,3,4,7,1,0,4}; ARR_SIZE will evaluate to 11

This is a useful code readability technique for things such as loops:

for(i=0;i< ARR_SIZE;i++); // is more readable

for(i=0;i< sizeof arr/sizeof arr[0];i++); // is less readable

Upvotes: 0

Arjun Mathew Dan
Arjun Mathew Dan

Reputation: 5298

Just a question/suggestion.

Do you really need "NUM_A" ? Atleast from the code snippet point of view, it is not required. Not sure if you are using it elsewhere for some other purpose.

You can declare the array as:

int Array[] = {A1, A2, A3}; /* So this becomes the only place to be modified, just add A4 in the future. No confusion with array size */

NUM_A is equivalent to "sizeof Array / sizeof Array[0]".

Example:

  int arr[] = {A1, A2, A3};
  int i;

  for(i = 0; i < sizeof arr / sizeof arr[0]; i++)
  {
    printf("%d\n", arr[i]);
  }

Upvotes: 1

Graham Borland
Graham Borland

Reputation: 60681

You can assert that the array is of the expected size:

assert(sizeof(Array) == NUMA * sizeof(Array[0]));

That's a runtime check. There are various ways of doing it at compile-time depending on your compiler version; see Static assert in C

Upvotes: 0

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