Thread: Data Structures Warning

I believe you are passing a variable that hasn't been created.

Basically...

Code:

// MUSIC FILE READING FUNCTION CALL
ReadMusicData(info); //error here

would at least need to be...

Code:

// MUSIC FILE READING FUNCTION CALL
CDInfo info;
ReadMusicData(info); //error here

but I think you have more problems than that in your code... because your 'info' variable wouldn't actually be populated after the 'ReadMusicData' function completes. This is because the 'ReadMusicData' function will actually read the data into a local copy of 'info' that doesn't get returned to outside the function.

You have two options...

1) Pass in a pointer to the ReadMusicData function

or

2) Return the populated CDInfo from the ReadMusicData function...

i.e. call the function in the following way...

Code:

CDInfo info = ReadMusicData();

Of course, you would have to update your ReadMusicData function as necessary.

Hope that helps.

Eddie

I declared my

Code:

CDInfo info;

in main.
I thought that structs did not need to be passed as pointers because they...were pointers. Maybe thats for an array of structs...

This does look like my problem though. Can someone show me how to pass the struct to a function using pointers?

I would think that it was like this:
declare

Code:

void ReadMusicData(CDInfo*);

call

Code:

ReadMusicData(&info);

definition

Code:

void ReadMusicData(CDInfo* info)

But I am getting this error now when I try to store variables.
C:\Program Files\Microsoft Visual Studio\MyProjects\Music2\music2.c(224) : error C2231: '.album' : left operand points to 'struct', use '->'

Never seen a "->" before what is it?

void ReadMusicData(CDInfo* p);

to access struct members using p.
p->artist;
p->album;
and so on.

Code:

void ReadMusicData(CDInfo info)   
{
// read in the title, author and then strip EOLNS 
 fgets ( info.artist, STRINGSIZE, inFile );
 fgets ( info.album, STRINGSIZE, inFile );
 info.artist [strlen (info.artist) - 1] = '\0';
 info.album [strlen (info.album) - 1] = '\0';
 
 fscanf(inFile, "%d", &info.numTracks);
 
 printf("Artist: %s\n", info.artist);
 printf("Album: %s\n", info.album);
 printf("Number of tracks: %d\n", &info.numTracks);
}

>printf("Number of tracks: %d\n", &info.numTracks);
&info.numTracks?

inFile needs to be defined.

Code:

ReadMusicData(info);

this is not needed.

This is what I have.

Code:

#include <stdio.h>  // includes standard in out library
#include <stdlib.h> // includes standard library
#include <time.h>   // includes system time library
#include <string.h> // includes the string library

#define ARRAYSIZE 15 // constant for the array size
#define BLANK ' '    // constant for blanks
#define QUITCHOICE 4 // constant to quit
#define STRINGSIZE 50 //constant for string sizes

// DATA TYPES
// assigns a data type cdName
typedef char CDName;

// assigns a data type cdName
typedef char String[STRINGSIZE];

// Assigns a data structure for file contents
typedef struct CDInfo		
{
	String artist;
	String album;
	int numTracks;
} CDInfo;


// FUNCTION PROTOTYPES
void PrintMenu(int*);

void ReadMusicData(CDInfo*);

void PlayInOrder( );

void PlayRandomOrder( );

void PlayOneTrack( ); 

void PrintClosing( );

/*==========================================================================*/
/* MAIN FUNCTION */

int main()
{ 
 // data type declarations for program arrays
 CDInfo info;

  // integer variable for menu choice
 int menuChoice = 0;

 PrintMenu(&menuChoice);

 // Error checks for 4
 while (menuChoice != 4)
	{
	// Call to function that reads in the array
	ReadMusicData(&info);
	// Switch to process user input
	switch (menuChoice)
			{
			// if 1 call to Play Function
			case 1: //PlayInOrder( );
					break;
			// If 2 call to Play Random Fuction
			case 2: //PlayRandomOrder( );
					break;
			// If 3 call to Play One Fuction
			case 3: //PlayOneTrack( );
					break;
			}
	// Call to print menu function
	PrintMenu(&menuChoice);

	} 
 // Checks for a 4 to quit
 while (menuChoice == QUITCHOICE)
	{
	 // Call to print closing function
	 PrintClosing();
	 // reset the menu choice to exit loop
	 menuChoice = 0;
	}
 // end of main returning 0 
 return 0;
}

/* ========================================================================== */
/* MENU PRINTING FUNCTION */

// This function recieves a variable integer from main and returns it by 
// simulated reference using pointers. The value is then processed by main
// to determine what the user wants to do.
void PrintMenu(int *menuChoice)
{
 // prints message
 printf ("\n************************************************************\n"
          "            WELCOME TO THE JLH05G MUSIC PLAYER!\n"          
         "************************************************************\n\n");
 // prints menu
 printf ("Please Choose a Menu Choice 1, 2, 3, or 4.\n"
	     "Then You Will Be Asked What File To Open.\n"
		 "1: Play Current Playlist In Order\n"
         "2: Play Randomized Playlist\n" 
         "3: Play One Song\n" 
         "4: Leave the Program\n");
 
 // inputs menu choice
 scanf("%d", menuChoice);
 // makes sure menu choice is valid
 while ((*menuChoice < 1) || (*menuChoice > 4))
	{
	// prints menu
	printf ("\nInvalid Menu Choice!\n"
		    "Please Choose a Menu Choice 1, 2, 3, or 4\n"
			"1: Play Current Playlist In Order\n"
			"2: Play Randomized Playlist\n" 
			"3: Play One Song\n" 
			"4: Exit the Program\n");
    // re inputs value
	scanf("%d", menuChoice);
	} 
 // echo prints users input
 printf("You chose %d\n\n", *menuChoice);
 // end of function return to main 
 return;
}// Function PrintMenu


/*==========================================================================*/
/* MUSIC FILE READING FUNCTION */

// This function reads from the file in to the array playList then reads from
// the file in to the typeCode to process what to store in the second array.
// It returns the arrays to main by simulated reference.
void ReadMusicData(CDInfo* info)  
{
// int lcv;
  // type for holding the file name
 CDName fileName[STRINGSIZE];
 // declares a file stream
 FILE* inFile;
 // print the message
 printf("Please Enter The File Name You Would Like To Open\n");
 // input users file
 scanf("%s", fileName);
 // echoprint user input
 printf("You Entered %s\n", fileName);
 // opens the file for read only
 inFile = fopen(fileName, "r");
 // test to make sure file opens 
 while (!fopen(fileName, "r"))
	{
	 // Prints Message
	printf("File Opening Failed!\n");
	// print the message
	printf("Please Enter The File Name You Would Like To Open\n");
	// input users file
	scanf("%s", fileName);
	// echoprint user input
	printf("You Entered %s\n", fileName);
	// opens the file for read only
	inFile = fopen(fileName, "r");
	} //while statement
 
 // prints the table
 printf("Your File Contents           #         Title\n"
		"------------------------------------------------\n");
 // read in the title, author and then strip EOLNS 
 fgets ( info->artist, STRINGSIZE, inFile );
 fgets ( info->album, STRINGSIZE, inFile );
 info->artist [strlen (info->artist) - 1] = '\0';
 info->album [strlen (info->album) - 1] = '\0';
 
 fscanf(inFile, "%d", info->numTracks);
 
 printf("Artist: %s\n", info->artist);
 printf("Album: %s\n", info->album);
 printf("Number of tracks: %d\n", info->numTracks);
 
 while(info->numTracks > ARRAYSIZE)
	{
    printf("Too Many Tracks!!\n");	
	}

// for ( lcv = 0; lcv < ARRAYSIZE; lcv++ )
// {
//
// }

}// Function ReadMusicData

Now I am getting a debug error. It crashes when it goes to input with fgets. I am new to structs can someone tell me what I am doing wrong or point me to a good tutorial?

Also if the number of tracks is bigger than 15 can I just call to the function again like this?

Code:

while(info->numTracks > ARRAYSIZE)
	{
        printf("Too Many Tracks!!\n");
	ReadMusicData(&info);
	}

Here is a sample data file:

Code:

Rolling Stones
A Very Short CD to Begin Testing Your Program
1
Start Me Up
3:32

> jlharrison
This user needs to read the forum rules
http://cboard.cprogramming.com/annou...ouncementid=51

And this moderator is closing the thread anyway.