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C++ std:: constructs in static library used by C program

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Started by Koshmaar August 12, 2005 12:36 PM

12 comments, last by Koshmaar 18 years, 8 months ago

Koshmaar

989

Author

August 13, 2005 05:15 PM

OMG, I'm dead!!! [bawling]

Hehe, just kidding ;-) There's #define CFG_String std::string, so changing only one line should suffice. Of course, assuming that I understood you correctly - change std::string to my own basic_string typedef with own allocator, recompile everything... and voila!

Btw, of course you are right, first I thought that those errors are both in std::string and std::map, but after examining all errors, it looks that maps are ok.

Quote:
as you are using a GCC compiler already you can just use __gnu_cxx::malloc_allocator in header ext/malloc_allocator.h as you can probably tell its uses malloc/free for allocation/deallocation instead but remember its not part of the standard its a GCC library extension so its trivial to define your own if you want.

Hmmm, there's no malloc_allocator.h in my MinGW 3.5(not standard GCC, I'm compiling on Win) compiler. Maybe I'm using (too) old version?
Anyway, you mentioned that its trivial to implement such allocator. I have in GPG #3 chapter about writing STL allocators, but anyway I'd like to see other examples (if you have any :-) ).

---

Btw, if any idiot ever said that error messagess in MinGW are user friendly... this snippet is for him:

(.text$_ZNSt14__simple_allocISt13_Rb_tree_nodeISt4pairIKSs18CFG_Internal_GroupEESt24__default_alloc_templateILb1ELi0EEE8allocateEj+0x2c):SDL_config.c: undefined reference to `std::__default_alloc_template<true, 0>::allocate(unsigned)'(.text$_ZNSt8_Rb_treeISsSt4pairIKSs18CFG_Internal_EntryESt10_Select1stIS3_ESt4lessISsESaIS3_EE14_M_create_nodeERKS3_+0x6f):SDL_config.c: undefined reference to `__cxa_begin_catch'(.text$_ZNSt8_Rb_treeISsSt4pairIKSs18CFG_Internal_EntryESt10_Select1stIS3_ESt4lessISsESaIS3_EE14_M_create_nodeERKS3_+0x8d):SDL_config.c: undefined reference to `__cxa_rethrow'(.text$_ZNSt8_Rb_treeISsSt4pairIKSs18CFG_Internal_EntryESt10_Select1stIS3_ESt4lessISsESaIS3_EE14_M_create_nodeERKS3_+0xb0):SDL_config.c: undefined reference to `__cxa_end_catch'(.text$_ZSt10_ConstructISt4pairIKSs18CFG_Internal_EntryES3_EvPT_RKT0_+0xc):SDL_config.c: undefined reference to `__gxx_personality_sj0'(.text$_ZStltIcSt11char_traitsIcESaIcEEbRKSbIT_T0_T1_ES8_+0x14):SDL_config.c: undefined reference to `std::string::compare(std::string const&) const'

That's exactly the same what snk_kid said post above, the only differenc is that's in compiler's language... ;-)

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snk_kid

1,312

August 13, 2005 05:42 PM

Quote:Original post by Koshmaar
Hmmm, there's no malloc_allocator.h in my MinGW 3.5(not standard GCC, I'm compiling on Win) compiler. Maybe I'm using (too) old version?
Anyway, you mentioned that its trivial to implement such allocator. I have in GPG #3 chapter about writing STL allocators, but anyway I'd like to see other examples (if you have any :-) ).

You could always update it [wink] if not here is an exact copy of the file:

// Allocator that wraps "C" malloc -*- C++ -*-// Copyright (C) 2001, 2002, 2003, 2004 Free Software Foundation, Inc.//// This file is part of the GNU ISO C++ Library.  This library is free// software; you can redistribute it and/or modify it under the// terms of the GNU General Public License as published by the// Free Software Foundation; either version 2, or (at your option)// any later version.// This library is distributed in the hope that it will be useful,// but WITHOUT ANY WARRANTY; without even the implied warranty of// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the// GNU General Public License for more details.// You should have received a copy of the GNU General Public License along// with this library; see the file COPYING.  If not, write to the Free// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,// USA.// As a special exception, you may use this file as part of a free software// library without restriction.  Specifically, if other files instantiate// templates or use macros or inline functions from this file, or you compile// this file and link it with other files to produce an executable, this// file does not by itself cause the resulting executable to be covered by// the GNU General Public License.  This exception does not however// invalidate any other reasons why the executable file might be covered by// the GNU General Public License.#ifndef _MALLOC_ALLOCATOR_H#define _MALLOC_ALLOCATOR_H 1#include <new>namespace __gnu_cxx{  /**   *  @brief  An allocator that uses malloc   *   *  This is precisely the allocator defined in the C++ Standard.    *    - all allocation calls malloc   *    - all deallocation calls free   *   *  (See @link Allocators allocators info @endlink for more.)   */  template<typename _Tp>    class malloc_allocator    {    public:      typedef size_t     size_type;      typedef ptrdiff_t  difference_type;      typedef _Tp*       pointer;      typedef const _Tp* const_pointer;      typedef _Tp&       reference;      typedef const _Tp& const_reference;      typedef _Tp        value_type;      template<typename _Tp1>        struct rebind        { typedef malloc_allocator<_Tp1> other; };      malloc_allocator() throw() { }      malloc_allocator(const malloc_allocator&) throw() { }      template<typename _Tp1>        malloc_allocator(const malloc_allocator<_Tp1>&) throw() { }      ~malloc_allocator() throw() { }      pointer      address(reference __x) const { return &__x; }      const_pointer      address(const_reference __x) const { return &__x; }      // NB: __n is permitted to be 0.  The C++ standard says nothing      // about what the return value is when __n == 0.      pointer      allocate(size_type __n, const void* = 0)      {	pointer __ret = static_cast<_Tp*>(malloc(__n * sizeof(_Tp)));	if (!__ret)	  throw std::bad_alloc();	return __ret;      }      // __p is not permitted to be a null pointer.      void      deallocate(pointer __p, size_type)      { free(static_cast<void*>(__p)); }      size_type      max_size() const throw()       { return size_t(-1) / sizeof(_Tp); }      // _GLIBCXX_RESOLVE_LIB_DEFECTS      // 402. wrong new expression in [some_] allocator::construct      void       construct(pointer __p, const _Tp& __val)       { ::new(__p) value_type(__val); }      void       destroy(pointer __p) { __p->~_Tp(); }    };  template<typename _Tp>    inline bool    operator==(const malloc_allocator<_Tp>&, const malloc_allocator<_Tp>&)    { return true; }    template<typename _Tp>    inline bool    operator!=(const malloc_allocator<_Tp>&, const malloc_allocator<_Tp>&)    { return false; }} // namespace __gnu_cxx#endif

Don't forget to include cstdlib where ever you use it.

snk_kid

1,312

August 13, 2005 06:30 PM

Actually that idea will still lead to problems (i think), i've never tried this myself before but after some playing around using something like malloc_allocator wont be enough you will still come across problems. I figured out that you can still use things like std::allocator and operator new/delete but you will need to link with libstdc++ on GCC when you finally compile an executable e.g.:

foo.h

#ifndef STD_STRING_H#define STD_STRING_H#ifdef __cplusplusextern "C" {#endif#include <stddef.h>typedef struct std_string std_string;std_string* string_construct(const char* s);char string_at(std_string* s, size_t index);void string_destroy(std_string* s);#ifdef __cplusplus};#endif#endif

foo.cpp

#include "foo.h"#include <string>struct std_string {   std::string s;   std_string(const char* cs): s(cs) {}};std_string* string_construct(const char* c) {   return new std_string(c);}char string_at(std_string* ss, size_t index) {   return ss->s[index];}void string_destroy(std_string* s) {    delete s;}

main.c

#include "foo.h"#include <stdio.h>int main() {   std_string* s = string_construct("hello");   printf("%c%c%c", string_at(s, 0), string_at(s, 1), string_at(s, 2));   string_destroy(s);}

Compile & Run:

g++ -O3 foo.cpp -cgcc -std=c99 -O3 foo.o main.c -o test -lstdc++./testhel

whether or not you want a dependance on libstdc++ in C is another story...

Koshmaar

989

Author

August 14, 2005 10:54 AM

Fortunately, I've managed to create static library project in VStudio, compile it, and then: successfully compile test programs BOTH in C++ and C.

What's strange, is that they compiled and linked WITHOUT specifing any additional allocators to std::string.

What's even more strange, is that test programs are working ;-) though sometimes there are crazy compiler errors in C version. Look at this code:

int main(int argc, char **argv) {  CFG_File config;  int result = CFG_OpenFile("test_001.cfg", &config );  /*if ( CFG_ERROR == result ) // (*)   {    fprintf(stderr, "Couldn't open file.");    return 1;   }  else if ( CFG_CRITICAL_ERROR == result )   {    fprintf(stderr, "Critical error: %s", CFG_GetError());    return 1;   }*/ // (**)    int value1 = CFG_ReadInt("screen_size_x", 101); (***) fprintf(stderr, "Integer value read from global group, entry *screen_size_x*: %i\n", value1 ); // (****) // ...

Above piece of code compiles and links without any problems, both in C and C++, on MinGW and VisualC++, with and without comments (*) and (**). However, when I remove comments from (*) and (**) and compile it in C on VisualC++, compiler complains:

(***) main.c(47) : error C2143: syntax error : missing ';' before 'type'(****) main.c(50) : error C2065: 'value1' : undeclared identifier

What's happening here? Even if I put ';' on closing '}', it still complains. BUT, if I copy n' paste lines (***) and (****) before first if, magically it's compiled without any problems... I don't what to think, probably it's trivial error connected with C syntax, which in this point differs with C++ and states that I should add sth here and there. Any thoughts?

---------

Ok, but enough this offtopic :-) let's go back to GCC. Snk_kid, I've done what you suggested: created malloc_allocator.h file with implementation you provided and added this code to library:

//#define CFG_GCC#ifdef CFG_GCC  #include <cstdlib>  #include <malloc_allocator.h>  #include <string>  typedef std::basic_string<char, std::char_traits<char>, __gnu_cxx::malloc_allocator<char> > CFG_Internal_String;  #define CFG_Internal_String_Arg const CFG_Internal_String &  #define CFG_String CFG_Internal_String#else  #define CFG_Internal_String_Arg const std::string &  #define CFG_String std::string#endif

When CFG_GCC is defined, if I compile library, I get problems with places, where any methods of CFG_Internal_String return std::string, and there is need to create from that returned string, new CFG_Internal_String. Hmmm, to be honest, it's actually only substr :-)

CFG_String groupName = parsed.substr(1, secondBracePos - 1);GCC says:error: conversion from `std::basic_string<char,    std::char_traits<char>, std::allocator<char> >' to non-scalar type `   std::basic_string<char, std::char_traits<char>,    __gnu_cxx::malloc_allocator<char> >' requestedVisual says:error C2440: 'initializing' : cannot convert from 'std::basic_string<_Elem,_Traits,_Ax>::_Myt' to 'std::basic_string<_Elem,_Traits,_Ax>'        with        [            _Elem=char,            _Traits=std::char_traits<char>,            _Ax=std::allocator<char>        ]        and        [            _Elem=char,            _Traits=std::char_traits<char>,            _Ax=__gnu_cxx::malloc_allocator<char>        ]        No constructor could take the source type, or constructor overload resolution was ambiguous

Well, quite logical. Substr() returns std::string, not const char * or even basic_string with allocator specified by user. Any ideas how to solve this problem? :-) If not, then on this site are listed functions that operate on std::string, especially copy, which copies string data to char array. Maybe after taking adress of begin() and sending it to copy, or playing with iterators, I could get it to work...

Btw, thanks for comments, snk_kid :-) sorry for no ++rating, but you were already maxed.

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