Pass value from one function to another
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Thread: Pass value from one function to another

  1. #1
    Join Date
    Oct 2013
    Posts
    2

    Pass value from one function to another

    In this program, I have to ask the user for an employee, then the program will check to see if the file for that employee exist, if it doesnt then it will automatically create the file.

    ReadNew function reads the file....check to see if it exist

    CreateNew function creates a new file.

    In my code I have no problem with the first part of reading file.. and my createnew function works in other programs where I am asking for input of file name to create the file name. However in this code I cannot figure how to automatically pass the input filename from the ReadNew function to the CreateNew function. I can't ask the user to enter the name a second time, so I have to pass the input filename into both functions

    Here is my code.
    Code:
    //Create a file, append to it, and read it.
    
    #include <iostream>
    #include <fstream>
    #include <string.h>
    #include <stdio.h>
    using namespace std;
    char filename[256];
    string n;
    string filelist;
    void CreateNew(ofstream & FileNew);
    void ReadNew(ifstream & FileGet);
    void AppendNew(ofstream & FileApp);
    int response;
    char trash[2];
    int fileyes=0;
    
    
    //Main
    int main()
    {	ofstream FileCreate;
        ifstream FileRead;
        ofstream fileAppend;
       
    	cout<<"Do you want to find information about an employee? (0 for yes, 1 for no) ";
    	cin>>response;
    	cin.getline(trash, 2);
    	while(response == 0)
    	
    	{ 
    		ReadNew(FileRead);
    	
    		if(fileyes==1)
    		{
    			CreateNew(FileCreate);
    		}	
    		cout<<"fileyes = "<<fileyes<<endl;	
    			
    	cout<<"enter another name (0 for yes, 1 for no)  ";
    	cin>>response;
    }	
    			
    
        return 0;
    }
    
    
    
    //functions
    
    void CreateNew(ofstream & FileNew)//Create file
    {
        char filename[256];
        string name;
        FileNew.open(filename);
        name = filename;
        if(FileNew.is_open())
        {
        	cout<<"\n";
            cout<<name<<".txt file is successfully created!\n";
    		cout<<"\n";
    		fileyes=0;
    		
        }
        else
            cout<<"can not open a file...\n"<<endl;
    }
    
    
    void ReadNew(ifstream & FileGet)// Read file
    {   char filename[256];
    	string name;
    	char newname;
        string line;
        fileyes=0;
       cout<<"Enter file name to extract info.: ";
       cin.getline(filename, 256);
       name = filename;
        FileGet.open(filename);
        if(FileGet.is_open())
        {
            while(1)
            {
                getline(FileGet, line);
                cout<<line<<endl;
    
                if(FileGet.eof())
                    break;
            }
        }
        else
        	fileyes=1;
           cout<<"read1\n ";
    }

  2. #2
    Join Date
    Dec 2012
    Location
    England
    Posts
    2,854

    Re: Pass value from one function to another

    If you want to request the name of the file in ReadNew, then the name can either be passed back to the calling routine as a return value from the function, or as a reference parameter to the function. Alternatively, but not recommended, name could be another global variable.

    A couple of points to note. For c++, the include names are cstring and cstdio, not string.h and stdio.h. Also, it is not considered good practice to have your variables defined as global. Good practice is to define them near to where they are first used with as small a scope as possible. Rather than have the file functions set a global variable, it would be more usual for these functions to return a type bool indicating whether success or not.

    eg
    Code:
    bool ReadNew(ifstream& FileGet, string& name)
    All advice is offered in good faith only. You are ultimately responsible for effects of your programs and the integrity of the machines they run on.

  3. #3
    Join Date
    Jul 2005
    Location
    Netherlands
    Posts
    2,016

    Re: Pass value from one function to another

    Code:
    #include <string.h>
    I guess you wanted the <string> header.
    Code:
    char filename[256];
    string n;
    string filelist;
    void CreateNew(ofstream & FileNew);
    void ReadNew(ifstream & FileGet);
    void AppendNew(ofstream & FileApp);
    int response;
    char trash[2];
    int fileyes=0;
    As 2kaud mentioned, using global variables is bad practice. Especially because you are using them to pass values between functions, which will prevent you from learning the proper way to pass values between functions and how to design your program. IMO it's also bad design to mix input/output with application logic. It would be better to split these things into separate functions. So, the outline of your program could be something like
    Code:
    std::string fileName = getFileName();
    std::ifstream ifs(fileName);
    if (!ifs.is_open()) {
        createFile(fileName);
        ifs.open(fileName);
    }
    displayContents(ifs);
    Code:
    	cout<<"Do you want to find information about an employee? (0 for yes, 1 for no) ";
    	cin>>response;
    What happens when the user inputs a letter? See Why does my program go into an infinite loop when someone enters an invalid input character?
    Cheers, D Drmmr

    Please put [code][/code] tags around your code to preserve indentation and make it more readable.

    As long as man ascribes to himself what is merely a posibility, he will not work for the attainment of it. - P. D. Ouspensky

  4. #4
    Lindley is offline Elite Member Power Poster
    Join Date
    Oct 2007
    Location
    Fairfax, VA
    Posts
    10,893

    Re: Pass value from one function to another

    Note that <string> and <cstring> are not the same.

    <cstring> is C++'s name for the old C <string.h>. It contains functions to operate on char*-style strings, like strcat, strcpy, etc.

    <string> is the C++ string class. It's much safer, easier, and all around better to use than char*s in most cases.

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