Short Story: With Current gcc/libstdc++ + uclibc you cannot put a float/double in a iostream (f.e. cout)
Attached Patch fix this, because the size of the allocated Buffer given to __convert_from_v is needed from uclibc. If GLIBCXX_C99 is defined libstdc++ give the cs_size to the function. Long Story: First i thought its an uclibc Bug: http://bugs.busybox.net/view.php?id=1090 The problem was: putting a double in a stream: cout << 10.5 ; Produce an empty string, or some garbage characters. Searchign the reason I found locale_facets.tcc the do_put impleemtation which is used for formating a double into a string in c++ iostream's. (gcc 4.2.1 : line 1143) but its in all gcc 4.x.x i looked . In the implementation the __convert_from_v the __cs_size is used. You can verify this with the following testCode #define protected public #include <iostream> using namespace std; int main() { float d=23.12; char * __cs = (char*) malloc(100); int __cs_size=100; char __fbuf[16]="%f"; const streamsize __prec = 6; __c_locale loc; locale::facet::_S_create_c_locale(loc, "C"); __convert_from_v(loc, __cs, 0, __fbuf, __prec, d); printf("test: %s\n",__cs); return 0; } This Fails in g++ + uclibc on a PowerPC Architecture. I hope I understand it correctly, i'm not very deep inside gcc/libstdc++ sources. --- gcc-4.2.1/libstdc++-v3/include/bits/locale_facets.tcc.orig 2007-08-27 11:19:50.000000000 +0200 +++ gcc-4.2.1/libstdc++-v3/include/bits/locale_facets.tcc 2007-08-27 11:19:52.000000000 +0200 @@ -1143,7 +1143,7 @@ const int __cs_size = __fixed ? __max_exp + __prec + 4 : __max_digits * 2 + __prec; char* __cs = static_cast<char*>(__builtin_alloca(__cs_size)); - __len = std::__convert_from_v(_S_get_c_locale(), __cs, 0, __fbuf, + __len = std::__convert_from_v(_S_get_c_locale(), __cs, __cs_size, __fbuf, __prec, __v); #endif -- Summary: libstc++ togehter wiht uclibc cannot format double in iostream Product: gcc Version: 4.2.1 Status: UNCONFIRMED Severity: major Priority: P3 Component: libstdc++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: g dot janak at unicontrol dot de GCC build triplet: powerpc-linux-uclibc GCC target triplet: powerpc-linux-uclibc http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33201
