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by okl
1 hour ago
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strncpy was originally used to write into fixed length buffers[1]. This becomes obvious when considering the padding behavior, as described in the C standard[2]: "If the array pointed to by s2 is a string that is shorter than n characters, null characters are appended to the copy in the array pointed to by s1, until n characters in all have been written." strlcpy, often touted as a replacement, does not elicit the padding behavior but has another flaw: It is supposed to return the length of the string it tried to create, for example, so the user can call realloc without calling strlen again.[3] However, this final "strlen-tail" in strlcpy isn't bounded by the size parameter which describes dest, not src. While strscpy is a marked improvement, there is still something to be careful about: It can read past the end of the src-buffer, when sizeof src < sizeof dest and src is not nul-terminated.[4] (Set the count argument to something like min(sizeof dest, sizeof src) to avoid that). -- [1] - https://softwareengineering.stackexchange.com/a/438090 [2] - https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3220.pdf, 7.26.2.5 p. 3 [3] - https://manpages.debian.org/jessie/libbsd-dev/strlcpy.3.en.h... [4] - https://manpages.debian.org/testing/linux-manual-4.8/strscpy... |
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