Thread: A class to contain structs

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;
	}
         //}

}

>>DataLine pDataSec;

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