Why is this an issue?
Declaring names in appropriate namespaces reduces the number of names found during lookup, decreasing the risk of name clash and of surprising name
lookup.
This rule raises an issue when a name in the global namespace has external linkage and therefore can be accessed from outside a particular
translation unit.
Some names have to be declared in the global namespace, and are excluded from this rule:
-
main (or its variants)
- Overloads of the global
new & delete operators
In addition, no issue is raised for function definitions because they can only be accessed from different translation units through a forward
declaration that will be flagged.
Noncompliant code example
int a; // Noncompliant
int b = 1; // Noncompliant
extern int c = 1; // Noncompliant
extern const int d = 1; // Noncompliant
void f(); // Noncompliant
class A { // Noncompliant
};
Compliant solution
namespace MY_API { // Compliant
int a;
int b = 1;
extern int c = 1;
extern const int d = 1;
void f();
class A {
};
} // namespace MY_API
namespace { // Compliant, anonymous namespace
int a = 1;
void m2() {
}
}
int main() { // Compliant, exception for main
}
static int a; // Compliant, internal linkage
static void m1(); // Compliant, internal linkage
const int a = 1; // Compliant, a global constant is implicitly static
extern "C" int a = 1; // Compliant
extern "C" void f1(); // Compliant
void f2() {} // Compliant
typedef int a; // Compliant, we don't detect aliases
void *operator new(size_t bytes, const X::Y& context) { return X::malloc(bytes,context); } // Compliant by exception
void operator delete(void* ptr, const X::Y& context) { X::free(bytes,context); } // Compliant by exception
Resources
- MISRA C++:2008, 7-3-1 - The global namespace shall only contain main, namespace declarations and extern "C" declarations.
