Why Are Trailing Commas Allowed in C Initializer Lists?

Redundant Commas in Initializer Lists

It may seem puzzling that C allows trailing commas in initializer lists, such as:

int a[] = {1, 2,};

Normally, redundant commas are not permitted in C , as seen in function argument lists:

// Syntax error
function_call(arg1, arg2,);

However, in the case of initializer lists, this restriction is explicitly lifted.

Rationale for Redundant Commas

This flexibility serves several purposes:

• Code Generation Simplification:
  It simplifies the process of generating source code by providing a uniform treatment for all list elements. No special handling is required for the last element.
• Easy Code Extension:
  Adding or removing elements from the list becomes more convenient when all elements already have trailing commas. No need to worry about altering the structure of the list.
• Code Transformation:
  It allows for easier reordering or other transformations of list elements without the need to modify the commas.

Code Example

Consider the following code:

int a[] = {
   1,
   2,
   3
};

To add an element to the list, you would only need to add a line:

int a[] = {
   1,
   2,
   3,
   4
};

Compare this to the case without trailing commas:

int a[] = {
   1
   2
   3
};

Adding an element would require modifying the existing line and adding a new line:

int a[] = {
   1
   2,
   3,
   4
};

Thus, allowing trailing commas in initializer lists reduces code complexity and improves maintainability.

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