From 05f913d57d6557d1c540894651cc83a5b1ec7cf7 Mon Sep 17 00:00:00 2001 From: Marc Mutz Date: Thu, 16 Feb 2023 15:48:17 +0100 Subject: qstrncpy: NUL-terminate even when src is nullptr MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The goal of this function is to ensure that dst is _always_ NUL-terminated. The only exception is if there's no space to write even one NUL byte, of course, but not when src is nullptr but dst would have space. Update the docs to the new behavior and make them more precise. Fix a test that assumed qstrncpy() would not write to dst for (dst, nullptr, 10). [ChangeLog][QtCore][qstrncpy()] Now NUL-terminates the target buffer even when the source pointer is nullptr, provided the target buffer has space for at least one byte. Pick-to: 6.5 6.4 6.2 5.15 Change-Id: I7806d8c71e260f8f02b79af7b6ce94f23599dd69 Reviewed-by: Qt CI Bot Reviewed-by: Thiago Macieira --- src/corelib/text/qbytearray.cpp | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) (limited to 'src/corelib/text') diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp index 75301f1f51..cd999d28f8 100644 --- a/src/corelib/text/qbytearray.cpp +++ b/src/corelib/text/qbytearray.cpp @@ -114,9 +114,9 @@ char *qstrcpy(char *dst, const char *src) A safe \c strncpy() function. Copies at most \a len bytes from \a src (stopping at \a len or the - terminating '\\0' whichever comes first) into \a dst and returns a - pointer to \a dst. Guarantees that \a dst is '\\0'-terminated. If - \a src or \a dst is \nullptr, returns \nullptr immediately. + terminating '\\0' whichever comes first) into \a dst. Guarantees that \a + dst is '\\0'-terminated, except when \a dst is \nullptr or \a len is 0. If + \a src is \nullptr, returns \nullptr, otherwise returns \a dst. This function assumes that \a dst is at least \a len characters long. @@ -128,9 +128,11 @@ char *qstrcpy(char *dst, const char *src) char *qstrncpy(char *dst, const char *src, size_t len) { - if (!src || !dst) - return nullptr; - if (len > 0) { + if (dst && len > 0) { + if (!src) { + *dst = '\0'; + return nullptr; + } #ifdef Q_CC_MSVC strncpy_s(dst, len, src, len - 1); #else @@ -138,7 +140,7 @@ char *qstrncpy(char *dst, const char *src, size_t len) #endif dst[len-1] = '\0'; } - return dst; + return src ? dst : nullptr; } /*! \fn size_t qstrlen(const char *str) -- cgit v1.2.3