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This noncompliant code example declares the msg identifier at file scope and reuses the same identifier to declare a character array local to the report_error() function. The programmer may unintentionally copy the function argument to the locally declared msg array within the report_error() function. Depending on the programmer's intention, this it either fails to initialize the global variable msg or allows the local msg buffer to overflow by using the global value msgsize as a bounds for the local buffer.

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This compliant solution uses different, more descriptive variable names.:

static char message[100];
static const size_t message_size = sizeof( message);

void report_error(const char *str) {
  char msg[80];
  snprintf(msg, sizeof( msg), "Error: %s\n", str);
  /* ... */
}

int main() {
  /* ... */
  report_error("some error");
}

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

Exceptions

DCL01-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);   // declarationDeclaration: no problem here
// ...
void f(char *arg) {   // definitionDefinition: no problem, arg doesn't hide name
  // use arg
}

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