C++ 从“char”到“const char *”的无效转换
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Invalid conversion from 'char' to 'const char *'
提问by NukingDragons
I am having trouble loading a char into one of my functions. This is the source code which I started out with.
我无法将字符加载到我的一个函数中。这是我开始使用的源代码。
main.cpp
主程序
#include <IOF\IOF.h>
int main()
{
char load;
string intro = LoadFileToString( "Intro.txt" );
cout << intro << "> ";
cin >> load;
string loadedFile = LoadFileToString( load );
cout << loadedFile;
cin.get();
cin.ignore();
return 0;
}
IOF.h
IOF.h
#ifndef IOF_H
#define IOF_H
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
string LoadFileToString( const char * filePath )
{
string fileData;
ifstream loadFile( filePath, ios::in );
if ( loadFile.is_open() )
{
string line;
while ( getline( loadFile, line ) )
{
fileData += line + "\n";
}
loadFile.close();
}
return fileData;
}
#endif
And this is what my compiler tells me.(I am using MinGW)
这就是我的编译器告诉我的。（我正在使用 MinGW）
H:\Programming\Dropbox\C++\Basic Text Editor\main.cpp: In function 'int main()':
H:\Programming\Dropbox\C++\Basic Text Editor\main.cpp:13:45: error: invalid conversion from 'char' to 'const char*' [-fpermissive]
string loadedFile = LoadFileToString( load );
^
In file included from H:\Programming\Dropbox\C++\Basic Text Editor\main.cpp:1:0:
H:\Programming\pocketcpp\MinGW\include/IOF\IOF.h:10:8: error: initializing argument 1 of 'std::string LoadFileToString(const char*)' [-fpermissive]
string LoadFileToString( const char * filePath )
I have tried referencing load, it compiles fine, but when I run the program and try to load a text file, it crashes. I have also tried adding a cast to it
我试过引用负载，它编译得很好，但是当我运行程序并尝试加载文本文件时，它崩溃了。我也试过给它添加演员表
string loadedFile = LoadFileToString( ( const char * ) load );
but that gave me this error:
但这给了我这个错误：
H:\Programming\Dropbox\C++\Basic Text Editor\main.cpp: In function 'int main()':
H:\Programming\Dropbox\C++\Basic Text Editor\main.cpp:13:57: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
string loadedFile = LoadFileToString( ( const char * ) load );
I originally made the IOF header so I would have a fast and easy way of receiving text from a file, but am I going to have to do all of the ifstream stuff manually for this part? Or is there a workaround?
我最初制作了 IOF 标头，因此我可以快速简便地从文件中接收文本，但是我是否必须为此部分手动执行所有 ifstream 操作？或者有解决方法吗？
回答by legends2k
char load;
string intro = LoadFileToString( "Intro.txt" );
cout << intro << "> ";
cin >> load;
string loadedFile = LoadFileToString( load );
You're trying to pass a charto LoadFileToStringwhich takes in a char*. I think what you intend to do is this
您正在尝试将 a 传递char给LoadFileToString一个接受 a char*。我想你打算做的是这个
string intro = LoadFileToString( "Intro.txt" );
cout << intro << "> ";
string load;
cin >> load;
string loadedFile = LoadFileToString( load.c_str() );
Notice that I'm reading the input into a stringinstead of a charsince the LoadFileToStringexpects a (C-style) string to be passed in; instead you're reading and trying to pass a character to it. Once the input is read through a string, a C-style string can be obtained by calling string::c_str()function.
请注意，我将输入读入 astring而不是 a，char因为LoadFileToString期望传入一个（C 样式）字符串；相反，您正在阅读并尝试将字符传递给它。通过 a 读取输入后string，可以通过调用string::c_str()函数获得 C 风格的字符串。
回答by Deduplicator
Never try to muzzle the compiler. Those warnings are invaluable. Obviously, you want a std::stringinstead of a char, where you define load.
永远不要试图压制编译器。这些警告是无价的。显然，您需要 astd::string而不是 a char，您可以在其中定义负载。
you get the const char*from a std::stringby calling c_str().
您可以通过调用const char*从 a获取。std::stringc_str()
Though, there is no reason your LoadFileToString()function should not instead take a const std::string&.
但是，您的LoadFileToString()函数没有理由不采用const std::string&.
回答by Vlad from Moscow
The error message is clear enough.
错误信息已经足够清楚了。
The function declared as
函数声明为
string LoadFileToString( const char * filePath );
that is its parameter has type const char *
那是它的参数有类型 const char *
You are trying to call the function passing variable load as an argument
您正在尝试调用传递变量负载作为参数的函数
string loadedFile = LoadFileToString( load );
However the variable load is declared as having type char
但是变量 load 被声明为具有类型 char
char load;
So there is a type mismatch.
所以存在类型不匹配。
You could for example to write
你可以例如写
string loadedFile = LoadFileToString( &load );
but in this case the code would be also invalid because the pointer referes to non zero-terminating string that is the behaviour of the program will be undefined.
但在这种情况下，代码也是无效的，因为指针指向非零终止字符串，即程序的行为将是未定义的。
