编译C程序时出错，该程序调用在头文件中声明并在单独的cpp文件中定义的C ++函数

问题描述

我正在尝试在C程序中调用C ++函数。我在.h文件中声明了该函数，如下所示： data_fields.h：

#ifdef __cplusplus
extern "C"
{
#endif
    char GetCharFromHexAscii(char *);
#ifdef __cplusplus
}
#endif

然后按如下方式在我的.c文件中调用GetCharFromHexAscii（）- GUIForRenamer.c：

#include<stdio.h>
#include<gtk/gtk.h>
#include<unistd.h>
#include<string.h>
#include<ctype.h>
#include"data_fields.h"
char * AsciiDecode(char *Path)
{
    int k = 0;
    char *convertedpath,*asciiChar;
    convertedpath = (char *)malloc(strlen(Path) + 1 * sizeof(char));
    asciiChar = (char *)malloc(3 * sizeof(char));
    for(int i = 0; Path[i] != '\0'; i++)
        convertedpath[k++] = GetCharFromHexAscii(asciiChar);
    return convertedpath;
}

.cpp中C ++函数的定义如下- LibFunc.cpp：

#include<iostream>
#include<cstdlib>
#include"data_fields.h"
char GetCharFromHexAscii(char *asciiChar)
{
    int hexVal = stoi(asciiChar,16);
    return (char)hexVal;
}

这是我用来编译C代码的命令-

gcc GUIForRenamer.c -lm `pkg-config --libs --cflags gtk+-3.0` -export-dynamic FileExtensionRenamer.c LibFunc.cpp

但是编译失败并出现以下错误-

LibFunc.cpp: In function ‘char GetCharFromHexAscii(char*)’:
LibFunc.cpp:7:15: error: ‘stoi’ was not declared in this scope
  int hexVal = stoi(asciiChar,16);
               ^~~~
LibFunc.cpp:7:15: note: suggested alternatives:
In file included from /usr/include/c++/7/string:52:0,from /usr/include/c++/7/bits/locale_classes.h:40,from /usr/include/c++/7/bits/ios_base.h:41,from /usr/include/c++/7/ios:42,from /usr/include/c++/7/ostream:38,from /usr/include/c++/7/iostream:39,from LibFunc.cpp:1:
/usr/include/c++/7/bits/basic_string.h:6477:3: note:   ‘std::__cxx11::stoi’
   stoi(const wstring& __str,size_t* __idx = 0,int __base = 10)
   ^~~~
/usr/include/c++/7/bits/basic_string.h:6477:3: note:   ‘std::__cxx11::stoi’

但是，如果我尝试通过在C ++程序中调用同一函数来进行编译，则编译会成功进行。

有人可以帮我弄清楚，对此还能做些什么？

基于以下建议，我对LibFunc.cpp中的代码进行了如下更新-

#include<iostream>
#include<cstdlib>
#include"data_fields.h"
#include<string>
using namespace std;
char GetCharFromHexAscii(char *asciiChar)
{
    int hexVal = stoi(asciiChar,16);
    return (char)hexVal;
}

在编译这段代码时，我遇到了以下问题-

/tmp/ccr7aSCZ.o: In function `GetCharFromHexAscii':
LibFunc.cpp:(.text+0x24): undefined reference to `std::allocator<char>::allocator()'
LibFunc.cpp:(.text+0x3b): undefined reference to `std::__cxx11::basic_string<char,std::char_traits<char>,std::allocator<char> >::basic_string(char const*,std::allocator<char> const&)'
LibFunc.cpp:(.text+0x60): undefined reference to `std::__cxx11::basic_string<char,std::allocator<char> >::~basic_string()'
LibFunc.cpp:(.text+0x6c): undefined reference to `std::allocator<char>::~allocator()'
LibFunc.cpp:(.text+0x8f): undefined reference to `std::__cxx11::basic_string<char,std::allocator<char> >::~basic_string()'
LibFunc.cpp:(.text+0xa0): undefined reference to `std::allocator<char>::~allocator()'
/tmp/ccr7aSCZ.o: In function `__static_initialization_and_destruction_0(int,int)':
LibFunc.cpp:(.text+0xe0): undefined reference to `std::ios_base::Init::Init()'
LibFunc.cpp:(.text+0xf5): undefined reference to `std::ios_base::Init::~Init()'
/tmp/ccr7aSCZ.o: In function `std::__cxx11::stoi(std::__cxx11::basic_string<char,std::allocator<char> > const&,unsigned long*,int)':
LibFunc.cpp:(.text._ZNSt7__cxx114stoiERKNS_12basic_stringIcSt11char_traitsIcESaIcEEEPmi[_ZNSt7__cxx114stoiERKNS_12basic_stringIcSt11char_traitsIcESaIcEEEPmi]+0x1b): undefined reference to `std::__cxx11::basic_string<char,std::allocator<char> >::c_str() const'
/tmp/ccr7aSCZ.o: In function `int __gnu_cxx::__stoa<long,int,char,int>(long (*)(char const*,char**,int),char const*,int)':
LibFunc.cpp:(.text._ZN9__gnu_cxx6__stoaIlicJiEEET0_PFT_PKT1_Pps3_DpT2_EPKcS5_PmS9_[_ZN9__gnu_cxx6__stoaIlicJiEEET0_PFT_PKT1_Pps3_DpT2_EPKcS5_PmS9_]+0x62): undefined reference to `std::__throw_invalid_argument(char const*)'
LibFunc.cpp:(.text._ZN9__gnu_cxx6__stoaIlicJiEEET0_PFT_PKT1_Pps3_DpT2_EPKcS5_PmS9_[_ZN9__gnu_cxx6__stoaIlicJiEEET0_PFT_PKT1_Pps3_DpT2_EPKcS5_PmS9_]+0xa3): undefined reference to `std::__throw_out_of_range(char const*)'
/tmp/ccr7aSCZ.o:(.data.rel.local.DW.ref.__gxx_personality_v0[DW.ref.__gxx_personality_v0]+0x0): undefined reference to `__gxx_personality_v0'
collect2: error: ld returned 1 exit status

我认为这是由于将char *作为参数而不是将字符串对象传递给stoi函数而导致的。因此，我将char *转换为字符串对象，并将其传递给函数。但是，这不能解决错误，并且仍然会出现相同的编译问题。

任何人都可以帮助我理解为什么会出现此错误，并提出解决该问题的方法吗？

解决方法

您调用函数stoi。您尚未定义此类功能。

就像也注意到了错误消息一样，您可能打算从C ++标准库调用std::stoi函数。请注意，它是在std命名空间中声明的。此外，您还应包括声明它的标头（<string>）。

此外，您可能需要链接到C ++标准库。如果您使用g++而不是gcc的前端，则会自动发生。

函数stoi位于<string>标头中（不是string.h，可以检查https://en.cppreference.com/w/cpp/string/basic_string/stol）。

由于代码中没有using namespace std，因此您应将对stoi的调用更改为std::stoi

最终的工作代码可能看起来像这样

#include <string>
char GetCharFromHexAscii(char *asciiChar)
{
    int hexVal = std::stoi(asciiChar,16);
     return (char)hexVal;
}

c c++extern