- If a regex evaluates to true call a member function (C++14) - 6 Updates
- Determining endianess at compile time - 11 Updates
- Removing Characters from basic::string - 4 Updates
- boolean string function to determine if the parentheses are balanced - 2 Updates
- If a regex evaluates to true call a member function (C++14) - 2 Updates
| ram@zedat.fu-berlin.de (Stefan Ram): May 15 04:08PM >and acts as an SCGI server. When an SCGI request comes from the HTTP If I'd have to do this, I'd ask for the grammar of the SCGI request language. If there is no such grammar, then it is not specified what I am actually supposed to implement. If there is such a grammar, then I can write a parser. Regular expressions are not always suitable to parse expressions. Are you sure that there is always at most one pattern that matches? Think about implementing it in the most natural way for now: if the request matches regexp0 then ... else if the request matches regexp1 then ... ... else if the request matches regexp9 then ... (This approach might not be suitable when there are very many such if-branches or the request syntax changes very often at runtime.) And hide it behind a concept (run-time interface). Once the whole system is working, you can then still "optimize" this part later /if/ need be. »Some people, when confronted with a problem, think "I know, I'll use regular expressions." Now they have two problems.« Jamie Zawinski in alt.religion.emacs |
| ram@zedat.fu-berlin.de (Stefan Ram): May 15 06:39PM >In practice it is easy: >Download boost and <boost/endian.hpp> figures it out compile time for fairly >decent list of platforms. Another means might be the Autoconf AC_C_BIGENDIAN feature. GNU C has »endian.h«, some systems have »sys/param.h«. |
| ram@zedat.fu-berlin.de (Stefan Ram): May 15 07:35PM > char ch = str.at(jj); > if(ch < 32) str.erase(jj, 1); >} #include <iostream> #include <ostream> #include <string> #include <algorithm> using namespace ::std::literals; int main() { ::std::string const source{ "alpha\0beta\0gamma"s }; ::std::string target; target.reserve( source.size() ); ::std::remove_copy_if ( source.begin(), source.end(), ::std::back_inserter( target ), []( ::std::string::value_type const ch ){ return !ch; }); ::std::cout << "target = " << target << '\n'; } |
| ram@zedat.fu-berlin.de (Stefan Ram): May 15 07:40PM >bind(not_equal_to, 0) or (with different, but maybe intended, semantics): #include <cctype> ... ::std::not1( ::std::ptr_fun( ::std::iscntrl )) . |
| ram@zedat.fu-berlin.de (Stefan Ram): May 15 07:43PM >#include <cctype> >... >::std::not1( ::std::ptr_fun( ::std::iscntrl )) What do you all think? When both notations are possible, is it better to use »point-free« notation (that is, without variables) or »lambda« notation? E.g., comparing bind( not_equal_to, 0 ) with []( int const point ){ return point != 0; } . |
| ram@zedat.fu-berlin.de (Stefan Ram): May 15 10:12PM >>decent list of platforms. >Another means might be the Autoconf AC_C_BIGENDIAN feature. >GNU C has »endian.h«, some systems have »sys/param.h«. The following code might not always yield the intended outcome as others have pointed out that some parts are not portable or well-defined, but it /is/ compiled with »constexpr«. #include <iostream> #include <ostream> constexpr bool endian() { using bytes = struct { char a; }; using overlay = union { int i; bytes b; }; return overlay{ 1 }.b.a; } int main() { ::std::cout << "endian()" << " = " << endian() << '\n'; } One could add security / sanity checks, such as statically asserting that sizeof( char)< sizeof( int ) or that one of the bytes is one and all preceding bytes are zero. |
| Juha Nieminen <nospam@thanks.invalid>: May 15 06:44AM Is it possible to determine endianess at compile time (in C++14)? At runtime it can be determined, for example, like this: bool isLittleEndianSystem() { unsigned value = 1; unsigned char* ptr = (unsigned char*)&value; return *ptr == 1; } Changing that to a constexpr function, however, doesn't seem so trivial (unless I'm missing something obvious). Any ideas? --- news://freenews.netfront.net/ - complaints: news@netfront.net --- |
| "Öö Tiib" <ootiib@hot.ee>: May 15 01:50AM -0700 On Friday, 15 May 2015 09:44:29 UTC+3, Juha Nieminen wrote: > } > Changing that to a constexpr function, however, doesn't seem so trivial > (unless I'm missing something obvious). Any ideas? Answer depends on if your question is of academical or of practical nature. In theory with standard C++ it is impossible: * There are no macros that help neither in C nor C++ ( and even not in POSIX). * 'std::numeric_limits' specify nothing about order of bits. * All the type punning through union or casts (that you need for manufacturing such check) are clearly listed as things that do *not* produce constant expressions by standard. In practice it is easy: Download boost and <boost/endian.hpp> figures it out compile time for fairly decent list of platforms. http://www.boost.org/doc/libs/1_58_0/boost/detail/endian.hpp |
| scott@slp53.sl.home (Scott Lurndal): May 15 02:32PM >Is it possible to determine endianess at compile time (in C++14)? on linux it is, regardless of the C++ version. Several of our C++ projects need to run on both LE and BE systems, we have this in a common header file then use the appropriate accessors in the code. Yes, it works with C as well. #include <endian.h> #ifndef __BYTE_ORDER #if defined(__BIG_ENDIAN) && !defined(__LITTLE_ENDIAN) #define __BYTE_ORDER __BIG_ENDIAN #elif !defined(__BIG_ENDIAN) && defined(__LITTLE_ENDIAN) #define __BYTE_ORDER __LITTLE_ENDIAN #define __BIG_ENDIAN 4321 #elif !defined(__BIG_ENDIAN) && !defined(__LITTLE_ENDIAN) #define __BIG_ENDIAN 4321 #define __BYTE_ORDER __BIG_ENDIAN #else #error Unable to determine Endian mode 
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