A class to contain structs

Hello,

I want to try and make something like this:

Code:

---

class FSAD        //Fixed/Selectable Analog Data 
        {
        public:

                char Name[25];
                int nExpected;  // size = nExected*2+1

                void MakeSec()
                {
                        DataLine *pDataSec;

                        pDataSec = new DataLine[nExpected*2+1];
                }
        };

---

Where the DataLine is:

Code:

---

struct DataLine
{
        char Param[20];
        int Label, SFactor, SigBits;
        int Bit30, Bit31, Max, Min;
} ;

---

If not sure if I call the constructor, How can I later access the variables in the array of structs inside the class?

The class is supposed to have two variables (char Name[25], int nExpected) and an array of structs (DataLine). I can't get to the individual variables inside the struct.
I tried using this and the compiler yelled at me:

Code:

---

Section.pDataSec[i].Param

---

Ideas?

Your code has a memory leak in it as you allocate a DataLine locally in MakeSec() (which, btw, cannot be accessed from outside MakeSec()), then fail to free it when it exits. Perhaps you want something like this:

Code:

---

struct DataLine{//everything public by default
        char Param[20];
        int Label, SFactor, SigBits;
        int Bit30, Bit31, Max, Min;
        DataLine(){//a REALLY GOOD IDEA to have a constructor initialize variables
                Label=SFactor=SigBits=Bit30=Bit31=Max=Min=0;
                memset(Param, 0, sizeof(Param));
        };
} ;

class FSAD{        //Fixed/Selectable Analog Data 
public:
        char Name[25];
        int nExpected;  // size = nExected*2+1
        DataLine dl;

        void MakeSec(){
                ;//use dl here
        };
};

FSDA Section;

strcncpy(Section.dl.Param, "something", 20);

---

I've realised that my array of structs was being destroyd once the program finishes with the constructor. I've fixed that same way you did.

Code:

---

class FSAD        //Fixed/Selectable Analog Data 
        {
        public:

                char Name[25];
                int nExpected;  // size = nExected*2+1
                DataLine *pDataSec;

                void MakeSec(DataLine *pDataSec)
                {
                        pDataSec = new DataLine[nExpected*2+1];
                }
        };

---

I think the problem comes from the way I pass it to a function. I'm writing a function to fill the array of structs. and I'm not sure how to pass the class to it correctly:

Code:

---

void ReadDataSec(FILE * inp, FSAD Section , int nExpected)
{
        char line[100];
        int  i=0;

        while ( fgets(line, sizeof line, inp) != NULL ) // reads in a line of text from file
        {
                //if ( strncmp(line, "ENDL", 4) == 0 ) // Exit if at the end of a section
                //{
                        sscanf(line, "%s", Section.pDataSec[i].Param);
                        printf("%s \n", Section.pDataSec[i].Param);

            break;
        }
        //}

}

---

If I don't use a function, and reference the array of stucts like this:

Code:

---

strncpy(FAD.pDataSec[0].Param, "something", 20);
        printf("%s\n", FAD.pDataSec[0].Param);

---

I get an run-time error that the memory could not be written.

First, you must provide a destructor to deallocate the memory you allocate for the struct array! Second, why not just use a vector instead, so you don't have to worry about deallocating the memory?

example:

Code:

---

struct DataLine{//everything public by default
        char Param[20];
        int Label, SFactor, SigBits;
        int Bit30, Bit31, Max, Min;
        DataLine(){//a REALLY GOOD IDEA to have a constructor initialize variables
                Label=SFactor=SigBits=Bit30=Bit31=Max=Min=0;
                memset(Param, 0, sizeof(Param));
        };
} ;

class FSAD{        //Fixed/Selectable Analog Data 
public:
        char Name[25];
        int nExpected;  // size = nExected*2+1
        vector < DataLine > vctDL;

        //void MakeSec() no need for this now
};

void ReadDataSec(FILE * inp, FSAD &Section , int nExpected)//note that Section MUST be passed in by reference!
{
        char line[100];
        int  i=0;
        DataLine dl;

        while ( fgets(line, sizeof line, inp) != NULL ) // reads in a line of text from file
        {
                //if ( strncmp(line, "ENDL", 4) == 0 ) // Exit if at the end of a section
                //{
                        sscanf(line, "%s",dl.Param);
                        printf("%s \n", dl.Param);
                        Section.vectDL.push_back(dl);//this does a copy, this could be more efficient with references, but I wouldn't worry about that now.

            break;
        }
        //}

}

---

If it's just one of the structs it's fine, But I need an array of them the size of which is determined at run-time.

and I never learned ho wto work with Vectors, I'll take a look at that.

I've read a few things about vectors,but I don't understand it enough to start playing with them.
After I've implemented all the suggestions to the best of my ability, this is what I came up with:

Function to work on the class:

Code:

---

void ReadDataSec(FILE * inp,class FSAD &Section , int nExpected)
{
        char line[100];
        int  i=0;

        GetWord(inp, &Section.pDataSec[0].Param);
        printf("%s\n\n", *Section.pDataSec[0].Param);

}

---

Class definition:

Code:

---

class FSAD        //Fixed/Selectable Analog Data 
        {
        public:

                char Name[25];
                int nExpected;  // size = nExected*2+1
                DataLine pDataSec;

                void MakeSec(DataLine *pDataSec)
                {
                        pDataSec = new DataLine[nExpected*2+1];
                };

                ~FSAD()
                {
                        delete[] pDataSec;
                };
        };

---

and the function call in main:

Code:

---

ReadDataSec(inp, FAD, FAD.nExpected);

---

and the problems, oh I hate them:

Code:

---

error C2440: 'delete' : cannot convert from 'struct DataLine' to ''
....
 error C2676: binary '[' : 'struct DataLine' does not define this operator or a conversion to a type acceptable to the predefined operator
H:\Code\EDFParse3\ReadDataSec.cpp(8) : error C2228: left of '.Param' must have class/struct/union type

---

>>DataLine pDataSec;

Did you forget a * to make pDataSec a pointer to type DataLine???

Its good practice, and maybe a "standard" for companies to have the variables in a class be private and have special get and set functions for the variables if needed.

I did forget a *. That's because I was trying all kinds of things to make it work, but nothing seems to.

Now a static array works, but a dynamic one through MakeSec call gives a run-time error, that memory could not be written.

And I'm not really worried about the public and private thing right now. I will look into that later if need be. thanks though.