linux ubuntu 下 ‘string’ was not declared in this scope 解析

linux ubuntu 下 ‘string’ was not declared in this scope 报错 解析

报错如下：

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test2.h:5:17: error: ‘string’ is not a member of ‘std’

aries@ubuntu:~/aries/Makefile/Demo$ g++ -o main main.cpp

In file included from main.cpp:1:0:

test1.h:5:17: error: variable or field ‘test1_cout’ declared void

test1.h:5:17: error: ‘string’ was not declared in this scope

In file included from main.cpp:2:0:

test2.h:5:17: error: variable or field ‘test2_cout’ declared void

test2.h:5:17: error: ‘string’ was not declared in this scope

aries@ubuntu:~/aries/Makefile/Demo$

ok！遇到问题我首先来一个个的排除问题

1

error.h

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#ifndef _ERROR_1_

#define _ERROR_1_

#include<cstring>



void cout_1(string a1);



#endif

error.c

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#include<error.h>

#include<iostream>

using namespace std;

void cout_1(string str)

{

cout << str<< endl;

}



int main()

{



cout_1("test");

return 0;



}

运行效果：

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aries@ubuntu:~/aries/Makefile/Demo$ g++ -o error error.cpp

aries@ubuntu:~/aries/Makefile/Demo$ ./error

test

2 把 main单独提出来看又会怎么样呢？

error_h.cpp

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#include<error.h>



void cout_1(string str)

{

cout << str<< endl;

}

修改error.c

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#include"error.h"

#include"error_h.cpp"

#include<iostream>

using namespace std;



int main()

{



cout_1("test");

return 0;



}

运行效果如下：

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aries@ubuntu:~/aries/Makefile/Demo$ g++ -o error error.cpp

In file included from error.cpp:1:0:

error.h:5:13: error: variable or field ‘cout_1’ declared void

error.h:5:13: error: ‘string’ was not declared in this scope

In file included from error.cpp:2:0:

error_h.cpp:3:13: error: variable or field ‘cout_1’ declared void

error_h.cpp:3:13: error: ‘string’ was not declared in this scope

error.cpp: In function ‘int main()’:

error.cpp:9:15: error: ‘cout_1’ was not declared in this scope

OK ！又出现上面的问题了。

疑问：为什么c++ 不可以 像c这样 呢？

3 我尝试了 google

然后上网找答案。在下面的几种情况下，会出现这种错误。

1.变量、函数、或者类未声明或者定义。这是最简单的情况。

2.头文件相互#include时，导致了依赖关系错误。比如，头文件形成了一个环形依赖，

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/***file a ****/

#ifndef FILE_A_

#define FILE_A_

#include <file b>

#endif



/****file b ***/

#ifndef FILE_B_

#define FILE_B_

#include <file a>

#endif

如果在file b中用到了file a中的变量、函数、类，那么由于#ifndef和#define的作用，file b中的#include <file a>语句将失去效果。

3.我遇到的情况：我在给头文件起名字的时候不小心和某个库中的头文件重名了，而在程序中又用来了这个库的这个头文件。这样， #ifndef XXXX 和 #ifndef XXXX中的宏重名了，我自己写的头文件就失去了效果。别的文件自然找不到这个头文件中的声明，就提示 was not decleared in this scope了。

仔细看了看，没有我想要的。

4 继续修改
error_h.cpp

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#include<error.h>

#include<cstring>

#include<iostream>

using namespace std;



void cout_1(string str)

{

cout << str<< endl;

}

运行效果如下：

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aries@ubuntu:~/aries/Makefile/Demo$ g++ -o error error.cpp

In file included from error.cpp:1:0:

error.h:5:13: error: variable or field ‘cout_1’ declared void

error.h:5:13: error: ‘string’ was not declared in this scope

还好错误减少了！不过还是error.h 报错。

我现在不知道如何修改了，求助！

--------------------------------------ok 已解决-----
代码如下：
error.h

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#ifndef _ERROR_1_

#define _ERROR_1_

#include<string>



void cout_1( std::string a1);



#endif

aries@ubuntu:~/aries/Makefile/Demo$

error_h.cpp

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#include<error.h>

#include<string>

#include<iostream>

using namespace std;



void cout_1( std ::string str)

{

cout << str<< endl;

}

main.c

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#include"error.h"

#include"error_h.cpp"

#include<iostream>

using namespace std;



int main()

{

std :: string a = "test";

cout_1(a);

return 0;



}

运行效果：



ok！ 结束

总结：我的原因是把 Cstring 是微软mfc的 搞成C++的头文件了
不过前面google 的还是很不错。

还得感谢我的老同学帮忙：

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#include"error.h"



#include"error_h.cpp"



#include<iostream>



using namespace std;







int main()



{



std :: string a = "test";



cout_1(a);



return 0;







}

有了using namespace std;就不用在string前加上他的：：了 你的博客写的不完美