尝试使用非恒定字符串使用freopen创建输出文件 [英] Trying to create an output file with freopen, using non-constant string

问题描述

我正试图创建一个文件，其名称为字符串常量，但由常量字符串"List"组成的字符串为整数+扩展名.这是我的代码:

I'm trying to create a file whose name is a string constant, but a string consisting of a constant string "List" an integer + + an extension. Here's my code:

#include <iostream>
#include <vector>
#include <iostream>
#include <fstream>
#include <iomanip>
#include <string>
using namespace std;

int main (){
            int cont=0;

            std::string result;
            std::string name = "Lista";
            std::string ext = ".txt";

            char numstr[21]; // enough to hold all numbers up to 64-bits
            sprintf(numstr, "%d", cont);
            result = name + numstr+ext;

            freopen (result, "w", stdout);
            cout<<result<<endl;
return 0;
}

当我尝试构建时会告诉我以下错误:

When I try to build tells me the following error:

错误:无法将std::string' to const char *'转换为参数1' to FILE * freopen(const char *，const char *，FILE *)'|

error: cannot convert std::string' toconst char*' for argument 1' toFILE* freopen(const char*, const char*, FILE*)'|

我该如何解决?

推荐答案

由于编译器错误指出，没有从std::string到char const*的隐式转换(即 c-style-string >在这种情况下.

As the compiler error states there is no implicit conversion from std::string to char const* (ie. a c-style-string in this context).

尽管std::string具有名为

Though std::string has a member-function named c_str which will generate a null-terminated string and return a pointer to it that is very usable when dealing with legacy C functions.

freopen (result.c_str (), "w", stdout);

char const * p = result.c_str ();

^{请注意，如果您对托管对象(在本例中为result)进行任何修改，则std::string::c_str指向的 c-style-string 将失效.将返回的值存储在非临时变量中通常是不明智的.}

^{Please note that the c-style-string pointed towards by std::string::c_str will be invalidated if you make any modifications to the hosting object (in this case result), therefore it is normally not wise to store the value returned in a non-temporary variable.}

如果您点击以下链接，则可以阅读有关该功能的更多信息:

• cppreference.com-std :: basic_string :: c_str

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