A little question
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From: nani on 5 Mar 2010 04:32 Using secured version of 'strcpy()' I need to use 'strcpy_s()' version and there lies my problem. In my function I need to copy the result in a char type which is passed to function. I pass a 'char addr[256]' but on my final step function: 'strcpy_s(addr, sizeof(addr), result)' the sizeof operator returns '4' and function chrases. The value of result is lets say an IP address (11 characters). What can I use instead 'sizeof' operater. I cant just use 256 because I use 'myfunction' in few places and passing different kind of char arrays. Sorry for english and thanks in advance
From: David Wilkinson on 5 Mar 2010 05:01 nani wrote: > Using secured version of 'strcpy()' I need to use 'strcpy_s()' version > and there lies my problem. In my function I need to copy the result in > a char type which is passed to function. I pass a 'char addr[256]' but > on my final step function: > 'strcpy_s(addr, sizeof(addr), result)' > the sizeof operator returns '4' and function chrases. The value of > result is lets say an IP address (11 characters). What can I use > instead 'sizeof' operater. I cant just use 256 because I use > 'myfunction' in few places and passing different kind of char arrays. > Sorry for english and thanks in advance An array decays to a char* pointer when passed to a function. That is why you see the size as 4. Your 'my function' needs to receive the size as a parameter. Or use std::string& as parameter instead of char*. -- David Wilkinson Visual C++ MVP
From: Joseph M. Newcomer on 5 Mar 2010 08:59 See below... On Fri, 5 Mar 2010 01:32:03 -0800 (PST), nani <cagalj.josip(a)gmail.com> wrote: >Using secured version of 'strcpy()' I need to use 'strcpy_s()' version >and there lies my problem. In my function I need to copy the result in >a char type which is passed to function. I pass a 'char addr[256]' but >on my final step function: >'strcpy_s(addr, sizeof(addr), result)' >the sizeof operator returns '4' and function chrases. The value of >result is lets say an IP address (11 characters). What can I use >instead 'sizeof' operater. I cant just use 256 because I use >'myfunction' in few places and passing different kind of char arrays. **** You must *always* pass in the size of the array, explicitly, as a parameter to the function! In fact, failure to do so can get you fired in certain companies today, because you would be violating secure coding practice. More below. **** >Sorry for english and thanks in advance **** Well, it did exactly what you asked, in exactly the correct way. If you pass a pointer to a buffer into a function, you must pass in the length explicitly (in fact, the implication that you "know" the length is a source of many errors). In modern practice, the ONLY correct way to pass a pointer to something to a subroutine that can fill in using strcpy, memcpy, etc. is to EXPLICITLY pass in the length: void DoCopy(char * p, size_t n, const char * value) { ... bunch of stuff strcpy_s(p, n, value); ...other stuff } You would call it as char addr[82]; DoCopy(addr, sizeof(addr), result); Your use of "sizeof" in *your* code says, explicitly, "the size of the object passed in is the size of a pointer". The fact that the pointer you used for the sizeof just happens to be the name of the parameter is irrelevant; you could have the same effect by having written strcpy_s(addr, sizeof(LPVOID), result); You can only use sizeof in contexts in which the compiler can know the size. It cannot know the size of a value pointed to by a parameter; it can only know the size of a variable based on its declaration. A pointer is implicitly declared to have a certain size. There isn't even a way for the compiler to determine if the parameter points to a character array, or something else, so there is no way it can figure out the size. sizeof() is evaluated entirely at compile time. So it did exactly what you asked it to do, it copy no more than sizeof(addr) characters, and sizeof(addr), given that addr is a char *, is 4 in Win32 (and 8 in Win64). Now, all that said, why are you (a) using fixed-sized buffers to do a copy of a string? (b) using the obsolete data type 'char'? (c) not writing Unicode-aware code? You should not use the 'char' data type except in rare and exotic circumstances, or when you are first bringing data into a program (such as using UTF-8 encoding) or writing it out. All code should be written as if it is in Unicode, or could be. So the data type should be TCHAR, and the function should be _tcscpy_s. In addition, using a fixed-size buffer is probably a mistake, nearly all the time. You should be using a CString. If I had to copy a value into a buffer, I would have written the code as void DoCopy(CString & dest, const CString & src) { ... stuff dest = src; ... } I am at the point where if I write a strcpy more than once a year or so, I'm doing something really odd and exotic. You should never think of char addr[256] as a natural way to express anything unless there is a *really* compelling reason for doing so (and there rarely is!). So why do you think you need a char array at all? joe **** Joseph M. Newcomer [MVP] email: newcomer(a)flounder.com Web: http://www.flounder.com MVP Tips: http://www.flounder.com/mvp_tips.htm
From: David Ching on 5 Mar 2010 14:12 "nani" <cagalj.josip(a)gmail.com> wrote in message news:6c60489f-7e30-49d2-a1a7-741a0b5e83ee(a)q16g2000yqq.googlegroups.com... > Using secured version of 'strcpy()' I need to use 'strcpy_s()' version > and there lies my problem. In my function I need to copy the result in > I pass a 'char addr[256]' but > on my final step function: > 'strcpy_s(addr, sizeof(addr), result)' > the sizeof operator returns '4' Are you sure? Last I checked: char addr[256]; assert (sizeof(addr) == 256); would not assert. -- David
From: Joseph M. Newcomer on 5 Mar 2010 14:57
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) { ... } joe On Fri, 5 Mar 2010 11:12:50 -0800, "David Ching" <dc(a)remove-this.dcsoft.com> wrote: >"nani" <cagalj.josip(a)gmail.com> wrote in message >news:6c60489f-7e30-49d2-a1a7-741a0b5e83ee(a)q16g2000yqq.googlegroups.com... >> Using secured version of 'strcpy()' I need to use 'strcpy_s()' version >> and there lies my problem. In my function I need to copy the result in >> I pass a 'char addr[256]' but >> on my final step function: >> 'strcpy_s(addr, sizeof(addr), result)' >> the sizeof operator returns '4' > >Are you sure? Last I checked: > > char addr[256]; > assert (sizeof(addr) == 256); > >would not assert. > >-- David Joseph M. Newcomer [MVP] email: newcomer(a)flounder.com Web: http://www.flounder.com MVP Tips: http://www.flounder.com/mvp_tips.htm |