strcpy_s copying more than string length to target buffer (filling with 0xFE)

Question

I have the following C++ code:

std::string test = "ABC";
char buffer[30];

for (int i = 0; i < 30; i++)
    buffer[i] = 0;

strcpy_s(buffer, 30, test.c_str());

After running it, I expect buffer to be: [0x41, 0x42, 0x43, 0x00, 0x00, 0x00, 0x00, ... 0x00] up to its end (29th position).

Running in VS2012, I´m getting the following result: [0x41, 0x42, 0x43, 0x00, 0xFE, 0xFE, 0xFE, ... 0xFE]

Why is strcpy_s copying more than my string length (3 chars + \0) ? Where is that 0xFE coming from ?

**...it may clobber the rest of the destination array with unspecified values...** Syntax 2) http://en.cppreference.com/w/c/string/byte/strcpy — Killzone Kid, Mar 13 '18 at 16:13

score 2 · Answer 1 · answered Mar 13 '18 at 16:13

2

This is allowed by strcpy_s:

strcpy_s is allowed to clobber the destination array from the last character written up to destsz in order to improve efficiency: it may copy in multibyte blocks and then check for null bytes.

answered Mar 13 '18 at 16:13

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What a detail! I will try some other method... Thanks. – Mendes Mar 13 '18 at 16:17

strcpy_s copying more than string length to target buffer (filling with 0xFE)

1 Answers1