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From: Qiang Ren <qiang.ren@microfocus.com> To: "gcc-bugs@gcc.gnu.org" <gcc-bugs@gcc.gnu.org> Subject: report a bug of gcc implementation of std::vsnprintf() Date: Thu, 30 Mar 2023 08:29:45 +0000 [thread overview] Message-ID: <DM6PR18MB27800EA091C72DDADC1354F9848E9@DM6PR18MB2780.namprd18.prod.outlook.com> (raw) [-- Attachment #1: Type: text/plain, Size: 1311 bytes --] Hi, I found a bug in the result of std::vsnprintf(), here is the test app that can reproduce it. I tested with g++ 11.2 and 12.2 and both have the bug, and this issue does not happen with visual c++. #include <stdio.h> #include <string> #include <iostream> #include <cstdarg> int Sprintf(std::string& s, const char* pszFormat, ...) { va_list argptr; va_start(argptr, pszFormat); auto n = std::vsnprintf(nullptr, 0, pszFormat, argptr); char* buf = (char*)malloc(n + 1); n = std::vsnprintf(buf, n + 1, pszFormat, argptr); s = buf; free(buf); va_end(argptr); return n; } int main() { std::string s, s0, s1, s2; double d = 3.14; //the result is wrong Sprintf(s, "abc%.0f", d); std::cout << "s=" << s << "\n\n"; //the result is wrong Sprintf(s0, "%.0f", d); std::cout << "s0=" << s0 << "\n\n"; //the printf result is correct printf( "%.0f\n\n", d); //now it becomes correct Sprintf(s1, "%.0f", d); std::cout << "s1=" << s1 << "\n\n"; //and this becomes correct too. Sprintf(s2, "abc%.0f", d); std::cout << "s2=" << s2 << "\n\n"; } In a short word, printf() get the correct result, after calling it, vsnprintf() became correct too. my build command: g++ -o t1 t1.cpp Thanks, Qiang Ren
next reply other threads:[~2023-03-30 8:29 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-03-30 8:29 Qiang Ren [this message] 2023-03-30 9:42 ` Jakub Jelinek
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