how to convert char to const char

[china_108]

I have a file which contains a year and the name of an associated file to be read.
I need to extract the data in the txt file and perform some calculations.
（ year data file）
2004 2004data.txt
2005 2005data.txt
2006 2006data.txt
...............................................
Here is what I do. I first declare "char yeardata" and then pass "2004data.txt" to it. Then I call yeardata in ifstream to extract the data inside the file "2004data.txt". The problem is that char yeardata is not constant so I cannot pass the file to it. It doesn't work if I change "char yeardata“ to ”const char yeardata”.

int oldnewcomp_temp(char* lcfile)
{
       using namespace std;
 
       int year;
       char yeardata;
  
      ifstream inFile2009b;
       inFile2009b.open(lcfile); 
       inFile2009b >>  year >> yeardata  ;
       inFile2009b.close();

   ......
   
    ifstream yearlydata;
      yearlydata.open(yeardata);
   ......
     
       yearlydata.close();
  
 return 0;
}

[ZuK]

yeardata is just a single character you need a std::string.
Then pass yeardata.c_str() to yearlydata.open(). Better still pass it to yearlidata's constructor.
Kurt

[Elkvis]

also, this is clearly C++, and you posted in the C forum. C and C++ are not the same thing. they are two very distinct languages.

[china_108]

Thanks a lot, Zuk. I am quite new to c++ and I need further explanation. I tried to convert "char yeardata" to " std::string yeardata" and then "yearlydata.open(yeardata)" to "yeardata.c_str()" but it doesn't work ........
Sorry for asking such a stupid thing.

[Elkvis]

I tried to convert "char yeardata" to " std::string yeardata" and then "yearlydata.open(yeardata)" to "yeardata.c_str()" but it doesn't work

explain how it doesn't work. "it doesn't work" is a very bad description of the problem, because it's impossible to help you with only that statement.

Sorry for asking such a stupid thing.

the only stupid question is the one that is not asked.

[china_108]

It is the same problem..... when I made the conversion, it says " cannot convert ‘std::string’ to ‘const char’ in initialization".

[laserlight]

Moved to C++ programming forum.

What is your current code?

[china_108]

int oldnewcomp_temp(char* lcfile)

{

       using namespace std;

  
       int year;
       std::string yeardata;

   
      ifstream inFile2009b;
       inFile2009b.open(lcfile); 
       inFile2009b >>  year >> yeardata  ;
       inFile2009b.close();
 
   ......
    
    std::ifstream yearlydata;

      yearlydata.open(yeardata.c_str());

   ......
      
       yearlydata.close();
   
 return 0;
}

[jimblumberg]

Look at the following snippet:

       char yeardata;
   
 ...   
    ifstream yearlydata;
      yearlydata.open(yeardata);

You defined yeardata as a single character, not a C-string. the ifstream.open() function requires a string, not a single character.

Also there is no need to use the open() function, just open it with the constructor. And I also recommend you use a std::string instead of the C-string.

    std::string yeardata;
...
//    ifstream yearlydata(yeardata); // If you have a C++11 compliant compiler.
//    ifstream yearlydata(yeardata.c_str()); // Otherwise.

Jim

[laserlight]

On which line does that error message refer to?

[china_108]

Thanks to laserlight, Jim, Elkvis and Kurt, I got it right now.

Thanks again!!!

[Elysia]

I suggest you avoid using char at all. They have a lot of gotchas and quirks which you must master in order to use them correctly and safely.
So what's the solution, then? 99% of the times, it's std::string.

[china_108]

yes, I used std::string
I forgot to add #include <string> at the beginning .......