A little question
in [MFC]
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From: David Ching on 5 Mar 2010 17:13 Right, I missed that he was doing that from the called function. Thanks, David "Joseph M. Newcomer" <newcomer(a)flounder.com> wrote in message news:2co2p5hujocjo2piv0nfapik0hieg3s3be(a)4ax.com... > But consider: > > char addr[256]; > DoSomething(addr); > > void DoSomething(char * addr) > { > ASSERT(sizeof(addr) == 256); // FAILS > ASSERT(sizeof(addr) == sizeof(DWORD_PTR)); // succeeds > ASSERT(sizeof(addr) == sizeof(LPVOID)); // succeeds > } > > Note that the example tries to use sizeof in the called function as if it > had meaning to > deliver the size of the buffer being pointed to, which, of course, it > cannot possibly do! > > The only correct solution is > > char addr[256]; > > DoSomething(addr, sizeof(addr)); > > void DoSomething(char * addr, size_t len) > { > ... > } >
From: Mihai N. on 6 Mar 2010 05:31
Everithing recomended in the previous posts is valid (you need to pass the size as a parameter). But I would recomend the discipline to use _countof instead of sizeof. 1. sizeof gives the size in bytes, so if you move to Unicode and char becomes wchar_t that will give the wrong result: TCHAR buffer[100]; sizeof(buffer) => 200 2. _countof complains at compilation if you try to apply it on a pointer, not an array. If _countof is not available (was added in VS 2005, I think), you can write your own simple version using templates, or just a macro (but then point 2 is not true anymore) #ifndef _countof #define _countof(a) (sizeof((a))/sizeof((a)[0])) #endif Mihai -- Mihai Nita [Microsoft MVP, Visual C++] http://www.mihai-nita.net ------------------------------------------ Replace _year_ with _ to get the real email |