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void f(void) {
  for (int i = 0; i < 10; i++) {
    long j;
    /* ... */
  }
}

Exceptions

DCL01-C-EX1: 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-C-EX2: A temporary variable within a new scope inside of a macro can override a surrounding identifieroverride an identifier in a containing scope. However,this exception does not apply to to the arguments of the macro itself.

#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 */
  SWAP(int, tmp, b); /* NONCOMPLIANT: Hidden redeclaration of tmp clashes with argument */
}

Risk Assessment

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

Automated Detection

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

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