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Discussion on: Effective C++ Programming: Best Practices and Common Pitfalls

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Thibaut Andrieu • • Edited

for 4) Avoid Global Use of using namespace

I would say "Never ever use using namespace in a header file".
using namespace in .cpp file is not that bad. But using it in header will contaminate all the file that include, directly or indirectly, this header. Ex (based on true story):

CustomMemoryManager.h

namespace CustomMemoryManager
{
   void* alloc();
   void free(void*)
}
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SomeFile.h

#include <CustomMemoryManager.h>
using namepace CustomMemoryManager;
...
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SomeOtherFile.h

#include <SomeFile.h>
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AgainAnotherFile.h

#include <SomeOtherFile.h>
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AndYetAnotherFile.cpp

#include <AgainAnotherFile.h>

void* ptr = std::malloc(...);

// [hundreds of line later]

free(ptr); // Oups... It build, maybe it even run, but it's actually CustomMemoryManager::free() which is called...
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And then, good luck to find the leak...