File pointer does not works when moved to a class? - c++

Question

So I found this solution to call a python script and it works in Microsoft Visual Studio Professional 2019 Version 16.6.2. I moved the three methods into a separate class and it no longer works. I thought I could figure it out but have just been beating myself up so I am here asking for help from readers who are much more knowledgeable than myself. The working code follows.
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>
#include <iostream>
#include <string>
void close_file(std::FILE* fp) {
std::fclose(fp);
}
std::string exec_python(const char* scriptCommand) {
std::array<char, 256> buffer;
std::string result;
std::unique_ptr<FILE, decltype(&close_file)> _pipe(_popen(scriptCommand, "r"), close_file);
if (!_pipe) {
throw std::runtime_error("popen() failed!");
}
while (fgets(buffer.data(), static_cast<int>(buffer.size()), _pipe.get()) != nullptr) {
result += buffer.data();
}
return result;
}
std::string call_script(std::string ScriptLoc, std::string Script_Parameters) {
std::string ScriptInput = ScriptLoc + " " + Script_Parameters;
std::string result = exec_python(ScriptInput.c_str());
return result;
}
int main()
{
std::string LOne = "python.exe \"C:\\Users\\.....\\source\\repos\\PyApplication1\\PyApplication1.py\"";
std::string LTwo = " Message";
//system(LTwo.c_str());
std::string oRez=call_script(LOne,LTwo);
std::cout <<"Results:"+oRez << std::endl;
}
The separate class that will not compile and related error messages follow. first is the header file, iTool.h.
#pragma once
#include <iostream>
#include <memory>
#include <stdexcept>
#include <string>
#include <array>
#include <iostream>
#include <string>
class iTool {
public:
void close_file(std::FILE* fp);
std::string exec_python(const char* scriptCommand);
std::string call_script(std::string ScriptLoc, std::string Script_Parameters);
iTool();
};
The second is the iTool.cpp.
#include "iTool.h"
void iTool::close_file(std::FILE* fp) {
std::fclose(fp);
}
std::string iTool::exec_python(const char* scriptCommand) {
std::array<char, 256> buffer;
std::string result;
std::unique_ptr<FILE, decltype(&close_file)> _pipe(_popen(scriptCommand, "r"), close_file);
if (!_pipe) {
//throw std::runtime_error("_popen() failed!");
} else { throw std::runtime_error("_popen() failed!"); }
while (fgets(buffer.data(), static_cast<int>(buffer.size()), _pipe.get()) != nullptr) {
result += buffer.data();
}
return result;
}
std::string iTool::call_script(std::string ScriptLoc, std::string Script_Parameters) {
std::string ScriptInput = ScriptLoc + " " + Script_Parameters;
std::string result = exec_python(ScriptInput.c_str());
return result;
}
iTool::iTool() = default;
The error messages.:
Severity Code Description Project File Line Suppression State
Error C2088 '!': illegal for class TestAppliance1 C:\Users\....\source\repos\TestAppliance1\iTool.cpp 11
Error C2276 '&': illegal operation on bound member function expression TestAppliance1 C:\Users\...\source\repos\TestAppliance1\iTool.cpp 10
Error C2514 'std::unique_ptr': class template cannot be constructed TestAppliance1 C:\Users\...\source\repos\TestAppliance1\iTool.cpp 10
Error C2660 'fgets': function does not take 2 arguments TestAppliance1 C:\Users\...\source\repos\TestAppliance1\iTool.cpp 14
Error C2662 '_Get_deleter_pointer_type<_Ty,remove_reference<_Ty1>::type,void>::type std::unique_ptr<_Ty,_Dx>::get(void) noexcept const': cannot convert 'this' pointer from 'std::unique_ptr' to 'const std::unique_ptr<_Ty,_Dx> &' TestAppliance1 C:\Users\...\source\repos\TestAppliance1\iTool.cpp 14
Thanks for your help!

Answer 1

You tripped over a non-static member function having a hidden this parameter and not matching the prototype expected for a deleter function.
Instead of void (*)(std::File*), the proposed deleter looks something like void (iTool::*(std::File*)
You can solve the problem by wrapping the function call with a lamda expression that captures this, but since close_file doesn't use this (something wrong with that--fp should probably be a member variable--that is outside the scope of this question), lets go with making it a static member function. The asker can clean up the ideological problems later.
In the iTool class definition,
void close_file(std::FILE* fp);
becomes
static void close_file(std::FILE* fp);

Answer 2

After you create a class you must create an instance of that class in the main function before you can use it:
iTool tool()
Inside you mean function.....
Also one word of caution for you my friend, if you do not know what:
iTool::iTool() = default;
Sets your variables to please do not use it...... You can always define those variables by yourself in your private part, if you know what the default does, by all means go ahead.