Page History

...

By using different variable names globally and locally, the compiler forces the developer to be more precise and descriptive with variable names.

Exceptions

DCL01-EX1EX0: A function argument in a function declaration may clash with a variable in a containing scope provided that when the function is defined, the argument has a name that clashes with no variables in any containing scopes.

extern int name;
void f(char *name);  /* Declaration: no problem here */
/* ... */
void f(char *arg) {  /* Definition: no problem; arg doesn't hide name */
  /* Use arg */
}

DCL01-EX1: A temporary variable within a new scope inside of a macro can override a surrounding identifier.

#define SWAP(type, a, b) do { type tmp = a; a = b; b = tmp; } while(0)
 
void func(void) {
  int tmp = 100;
  int a = 10, b = 20;
  SWAP(int, a, b); /* Hidden redeclaration of tmp is acceptable */
}

Risk Assessment

Reusing a variable name in a subscope can lead to unintentionally referencing an incorrect variable.

...