C++ - strcpy_s() always fails even if copying just one byte to big buffer

Question

I feel like I've always used strcpy to copy strings without having any trouble, but I haven't done it for a long time and now I can't get it to work no matter what I do.

I'm sure there's something dumb I'm missing, but I've been frustrated with this for a while so I'm here to see if anybody else can help.

const char* src = "Lalalala";
int strLen = strlen(src);
char* dest = new char[strLen + 1];
ZeroMemory(dest, strLen + 1);
strcpy_s(dest, strLen, src);

This code throws me an exception saying that the lBuffer is too small. Even if I try copying just "one byte" of data, and allocate a buffer of 128 bytes, it throws the same exception.

Also, I've checked that strlen returns the expected value, the allocation and the "ZeroMemory" function call work fine, and it's only when running the strcpy_s() function that the program crashes. I don't know what's going on here, please help!

Thanks

I can, in fact, I am using it right now in order to get the program to work. I'm just curious at what could be wrong with that code. Before learning to use the STL I would do a bunch of things that way and based on my memory and research that should work. So I'm just frustrated that it isn't and I'm wondering if anybody would have an idea why. — danielmlima, Nov 12 '15 at 16:33
Since I couldn't get it to work I kind of just started trying some random stuff, like cleaning up the buffer first, seeing if that was working fine, etc. — danielmlima, Nov 12 '15 at 16:42
`strcpy_s` does not throw exceptions. Please detail what you mean when you say it *"throws me an exception"*. — abelenky, Nov 12 '15 at 16:50

score 5 · Accepted Answer · answered Nov 12 '15 at 16:36

The second parameter of strcpy_s is numberOfElements. This is the buffer size, not string length.

From MSDN:

numberOfElements
     Size of the destination string buffer in char units for narrow and multi-byte functions, and wchar_t units for wide functions.

When you call strcpy_s in your example above, you're passing 8 as the length of the buffer, but strcpy_s wants to copy 9 characters. 8 characters of the string + 1 null terminator. It sees the buffer isn't big enough, and throws.

Try passing strLen + 1 which is the actual size of the buffer. Should work there.

That was it, thank you so much! I thought that since I had called ZeroMemory before it already had the null terminator so I only needed to copy the 8 regular characters and leave that as is. I didn't realize that's what the second parameter meant. Thank you again! ;) — danielmlima, Nov 12 '15 at 16:43

C++ - strcpy_s() always fails even if copying just one byte to big buffer

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