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If a file-scope object or a function does not need to be visible outside of the file, it should be hidden by being declared as static. This creates more modular code and limits pollution of the global name space.

Section 6.2.2 of C99 of the C standard [ISO/IEC 9899:19992011] states that:

If the declaration of a file scope identifier for an object or a function contains the storage-class specifier static, the identifier has internal linkage.

...

enum { MAX = 100 };

int helper(int i) {
  /* perform some computation based on i */
}

int main(void) {
  size_t i;
  int out[MAX];

  for (i = 0; i < MAX; i++) {
    out[i] = helper(i);
  }

  /* ... */

}

...

enum {MAX = 100};

static int helper(int i) {
  /* perform some computation based on i */
}

int main(void) {
  size_t i;
  int out[MAX];

  for (i = 0; i < MAX; i++) {
    out[i] = helper(i);
  }

  /* ... */

}

...

Related Vulnerabilities

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

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CERT C++ Secure Coding Standard: DCL15-CPP. Declare file-scope objects or functions that do not need external linkage in an unnamed namespace

ISO/IEC 9899:19992011 Section 6.2.2, "Linkages of identifiers"

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