I'm afraid closing this issue as Won't Fix is not appropriate. We do need to fix it.
The C++ standard says the num_put face behaves "as if" if it called sprintf with the specified format directive. The C standard, in turn, specifies the exact output to be produced. That fact that Microsoft's implementation of sprintf() fails to conform to the requirements of the C standard doesn't mean we don't have to. Rather it means that we cannot rely of Microsoft's sprintf() to implement the facet and instead have to code it "as if" it were implemented in terms of a sprintf() that does conform. Btw., avoiding sprintf() and writing our own formatting routine might actually yield more efficient code (the performance of floating point I/O is one of stdcxx weaknesses). Martin Farid Zaripov (JIRA) wrote:
[ https://issues.apache.org/jira/browse/STDCXX-2?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ] Farid Zaripov resolved STDCXX-2. -------------------------------- Resolution: Won't FixThe problem in the MSVC CRT.The expression strm << 0.0; is invokes the __rw_put_num() function, where used the CRT function snprintf() (num_put.cpp, line 752): snprintf (buf, size, "%#.2lg", 0.0); The result of the snprintf() call above is: "0.00". Info from MSDN: ----------------------------- Flag '#' means: When used with the g or G format, the # flag forces the output value to contain a decimal point in all cases and prevents the truncation of trailing zeros. The precision (".2") means: The precision specifies the maximum number of significant digits printed. ----------------------------- The prefix 'l' before type character 'g' here should point to the long double type, but passed double number (0.0). Anyway this is not causes any problem because of the types double and long double have the same internal representation on the MSVC.[MSVC] std::num_put bad formatting of 0.0 with precision and showpoint ---------------------------------------------------------------------- Key: STDCXX-2 URL: https://issues.apache.org/jira/browse/STDCXX-2 Project: C++ Standard Library Issue Type: Bug Components: 22. Localization Affects Versions: 4.1.2 Environment: Windows/MSVC Reporter: Martin Sebor Assignee: Farid Zaripov When compiled with MSVC (any version), the program below aborts at runtime. $ cat t.cpp && cl -D_RWCONFIG=11s_msvc_7_1 -Ic:/contrib/cygwin/build/sebor/dev-hal/include -I./../../../../include -Ic:/contrib/cygwin/build/sebor/dev-hal/examples/stdlib/manual/../include -Ic:/contrib/cygwin/build/sebor/dev-hal/include/ansi -I./../../../.. -Ic:/contrib/cygwin/build/sebor/dev-hal -Ic:/contrib/cygwin/build/sebor/dev-hal/examples/stdlib/manual -I. -nologo -GX -MLd -W3 -Zi -GA -GR -GF -GZ -c t.cpp && link -nologo /NODEFAULTLIB:libcpd /debug /LIBPATH:./../../../../lib /OUT:t.exe t.obj std11s_msvc_7_1.lib user32.lib t.cpp && ./t.exe #include <cassert> #include <sstream> int main () { std::ostringstream strm; strm.setf (strm.showpoint); strm.precision (2); strm << 0.0; assert ("0.0" == strm.str ()); } Assertion failed: "0.0" == strm.str (), file t.cpp, line 13
