Common GCC Attributes

Tue, 13 Aug 2024 21:13:45 +0200

Function attributes

fallthrough

The fallthrough attribute with a null statement serves as a fallthrough statement. It hints to the compiler that a statement that falls through to another case label, or user-defined label in a switch statement is intentional and thus the -Wimplicit-fallthrough warning must not trigger.

For compatibility with GCC and Clang you can also use // fall through or // fallthrough.

switch(cond)
{
case 1:
  bar(1);
    __attribute__((fallthrough));
  case 2:
    …
}

deprecated & deprecated (msg)

The deprecated attribute results in a warning if the function is used anywhere in the source file. This is useful when identifying functions that are expected to be removed in a future version of a program. The warning also includes the location of the declaration of the deprecated function, to enable users to easily find further information about why the function is deprecated, or what they should do instead.

What is the difference between `char a[]` and `char *p`

Wed, 28 Feb 2024 21:24:23 +0200

The Array version:

char a[] = "string";

Creates an array that is large enough to hold the string literal string, including its NULL terminator. The array string is initialized with the string literal string. The array can be modified at a later time. Also, the array’s size is known even at compile time, so sizeof operator can be used to determine its size.

The pointer version:

char *p  = "string";

Creates a pointer to point to a string literal “string”. This is faster than the array version, but string pointed by the pointer should not be changed, because it is located in a read only implementation-defined memory. Modifying such an string literal results in Undefined Behavior.