System（）没有合适的转换C ++ [英] System() no suitable conversion C++

问题描述

我有两个文件名列表。

std::list<std::string> userfontlist;
std::list<std::string>::iterator it;
std::list<std::string> CAATfontlist;
std::list<std::string>::iterator it2;
std::list<std::string> doesnthavelist;

，我想比较2个列表，并删除它匹配的值。每个似乎都很好，直到我添加del / F / Q / A到y.c_string（）。

and I want to compare the 2 lists, and delete the value it matches. every seems to be fine until I add the "del /F /Q /A" to the y.c_string().

for (it = userfontlist.begin(); it !=userfontlist.end(); ++it){
    for(it2 = CAATfontlist.begin();it2 !=CAATfontlist.end();++it2){
        if(*it==*it2){
            string y = *it;
            string k = y.c_str();
            string a = "del /F /Q /A " + k;
            system(a);

        }
    }
 }

a）说我有没有合适的转换函数从std字符串到const char *存在。如果我把整个东西作为1字符串，它工作，但不是当我连接字符串和y.c_str（）。我没有运气试图将std :: string转换为const * char，甚至不确定如果这甚至有帮助。

system(a) Says I have "no suitable conversion function from std string to const char * exists". If I put the whole thing as 1 string it works, but not when I concatenate the string and the y.c_str(). I have had no luck trying to convert the std::string to const *char, not even sure if that even helps.

推荐答案

正如它所说，没有理解 std :: string 和<$ c $的版本 system（） c> std :: string 不能自由转换为 const char * （其中 system c $ c>确实理解），因为 std :: string 可能会在一般情况下没有意义的方式消失。

exactly as it says, there's no version of system() that understands std::string and std::string can't be freely converted to const char * (which system() does understand), because std::string may go away in ways that don't make sense in the general case.

您可以显式地从 std :: string 转换为 const char * 很容易，但是： std :: string :: c_str ，将最后一行写为

you can explicitly convert from std::string to const char * easily, though: with std::string::c_str, write your last line as

system(a.c_str());

请注意返回的 const char * 的生命周期与 string 有关，一旦超出范围，指针就会变得无效。这个case是一个很好的时间使用它，虽然，因为 system（）不会保持指针超过自己的返回。

Be aware that the returned const char *'s lifetime is tied to the string it came from, once it goes out of scope, the pointer becomes invalid. This case is a fine time to use it, though, since system() won't "hold on" to the pointer past its own return.

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