Thread: need some help with writing and reading to/from a file

Hi,

I have the following C "program" that I've been working on for a while now. It's pieced together from my book and some code tidbits I've found on various forums.

It runs, but it is not working correctly.

It generates duplicates when I add tool records and when listing tools, it generates output that looks like this:

1 hammer -858993460 -858993460
25 -858993460 -858993460
50
-858993460 -858993460
1 hammer -858993460 -858993460
25 -858993460 -858993460
50
-858993460 -858993460

I've tried coding it in different ways, but they all seem to end up worse than this version.

Here is the non-erring version. If anyone could help, I'd greatly appreciate it.

Thanks!

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>




struct hardwareData 
{
	int recordNum;
	char toolname[20];
	int quantity;
	int cost;
}; 


/* prototypes */
int enterChoice( void );
void textFile( FILE *readPtr );
void updateRecord( FILE *fPtr );
void newRecord( FILE *fPtr );
void deleteRecord( FILE *fPtr );


int main()
{
  FILE *cfPtr; 
  cfPtr = fopen( "hardware.dat", "w" );
  int choice;


  
	if ((cfPtr = fopen( "hardware.dat", "rb+" )) == NULL ) 
	{
		printf( "File could not be opened.\n" );
	}
	else 
	{
		while (( choice = enterChoice()) != 5 ) 
		{
 			switch ( choice ) 
			{
				/* create text file from record */
 				case 1: 
				textFile( cfPtr );
				break;


				/* update record */
 				case 2: 
				updateRecord( cfPtr );
				break;


				/* create record */
 				case 3:
				newRecord ( cfPtr );
				break;


				/* delete existing record */
 				case 4:
				deleteRecord ( cfPtr );
				break;


				/* display message if user does not enter valid choice */
 				default:
				printf( "Incorrect choice\n" );
				break;


 			} 
		} 
		fclose( cfPtr ); 
	} 
	return 0; 
} 


void textFile( FILE *readPtr )
{
	FILE *writePtr;


	struct hardwareData hardware = { 0, "", 0, 0 };


	if ((writePtr = fopen( "hardware.txt", "w" )) == NULL ) 
	{
		printf( "File could not be opened.\n" );
	} 
	else
	{ 
		rewind( readPtr );
		/* copy all records from random-access file to text file */
		while ( !feof( readPtr ) ) 
		{
 			fread( &hardware, sizeof( struct hardwareData ), 1, readPtr );
 			/* write single record to text file */
 			if ( hardware.recordNum != 0 ) 
			{
				fprintf(writePtr, "%d %s %d %d\n", hardware.recordNum, hardware.toolname, hardware.quantity, hardware.cost );
 			}
			else
			{
				printf("File is empty.\n");
			}
		} 
		fclose( writePtr );
	} 
	writePtr = fopen( "hardware.txt", "r" );


	int toolNumber;
	char toolName[20];
	int toolQuanity;
	int toolCost;


	while ( !feof( writePtr ) ) {
		fscanf( writePtr, "%d%[^0-9-]&d%d", &toolNumber, toolName, &toolQuanity, &toolCost );
		printf( "%d %s %d %d\n", toolNumber, toolName, toolQuanity, toolCost );
	}
	fclose( writePtr );
} 


void updateRecord ( FILE *fPtr )
{
	int record; 
	struct hardwareData hardware = { 0, "", 0, 0 };


	printf( "Enter record to update (1-100): ");
	scanf( "%d", &record );


	
	fseek( fPtr, ( record - 1 ) * sizeof( struct hardwareData ), SEEK_SET );


	fread( &record, sizeof( struct hardwareData ), 1, fPtr );


	if ( hardware.recordNum == 0) 
	{
 		printf( "Record #%d has no information.\n", record );
	}
	else 
	{ /* update record */
 		printf( "Enter new tool name, quantity,cost \n?" );
 		scanf( "%s%d%d", hardware.toolname, &hardware.quantity, &hardware.cost );
     
 		fseek( fPtr, ( record - 1 ) * sizeof( struct hardwareData ), SEEK_SET );
		/* write updated record over old record */
 		fwrite( &hardware, sizeof( struct hardwareData ), 1, fPtr );
	} 


} 


void deleteRecord( FILE *fPtr )
{
	struct hardwareData hardware; 
	struct hardwareData blankRecord = { 0, "", 0,0 };
	int recordNum; 


	
	printf( "Enter record number to delete (1-100): " );
	scanf( "%d", &recordNum );


	fseek( fPtr, ( recordNum - 1 ) * sizeof( struct hardwareData ), SEEK_SET );


	fread( &hardware, sizeof( struct hardwareData ), 1, fPtr );
  
	if ( hardware.recordNum==0 ) 
	{
		printf ( "Record %d does not exist.\n", recordNum );
	} 
	else 
	{ 
		fseek( fPtr, ( recordNum - 1 ) * sizeof( struct hardwareData ), SEEK_SET );
		fwrite( &blankRecord, sizeof( struct hardwareData ), 1, fPtr );
	} 
} 


void newRecord( FILE *fPtr )
{
	struct hardwareData hardware = { 0, "", 0, 0 };
	int piece; 


	printf( "Enter record number to create (1-100) : " );
	scanf( "%d", &piece);
	
	fseek( fPtr, (piece - 1) * sizeof( struct hardwareData ), SEEK_SET );


	fread( &hardware, sizeof( struct hardwareData ), 1, fPtr );


	if ( hardware.recordNum != 0 ) 
	{
		printf( "Record already exists.\n", hardware.recordNum );
	}
	else 
	{ 


		printf( "Enter tool name, quantity, cost\n?" );
		scanf("%s%d%d", hardware.toolname, &hardware.quantity, &hardware.cost);


		hardware.recordNum = piece;


		fseek(fPtr, (hardware.recordNum-1) * sizeof( struct hardwareData), SEEK_SET);


		fwrite( &hardware, sizeof( struct hardwareData), 1, fPtr);
	} 
} 
 
int enterChoice( void )
{
	int menuChoice;
	printf( "\nEnter your choice\n"
			"1 - List of all tools\n"
			"2 - Update an existing tool\n"
			"3 - Add a new tool\n"
			"4 - Delete a tool\n"
			"5 - End program\n? " );
	scanf( "%d", &menuChoice ); 
	return menuChoice;
}

You may want to insure your compiler is generating warnings:

main.c||In function ‘textFile’:|
main.c|122|warning: too many arguments for format|
main.c||In function ‘newRecord’:|
main.c|210|warning: too many arguments for format|
||=== Build finished: 0 errors, 2 warnings ===|

These warnings may be one source of your problems.

Jim

Originally Posted by jimblumberg

You may want to insure your compiler is generating warnings:


These warnings may be one source of your problems.

Jim

Thanks....but each of those functions takes one argument and I am only passing one argument to them. So I don't see how those errors could be getting generated.

Thank you for taking the time to look at the code.

Originally Posted by hk_mp5kpdw

Code:

rewind( readPtr );
/* copy all records from random-access file to text file */
while ( !feof( readPtr ) )
{
    fread( &hardware, sizeof( struct hardwareData ), 1, readPtr );

Read: Why it's bad to use feof() to control a loop

Oh I see...ok I will try and replace "!feof" with "fgets(buf, sizeof(buf), fp) != NULL"

Thank you!

Thanks....but each of those functions takes one argument and I am only passing one argument to them. So I don't see how those errors could be getting generated.

main.c|122|warning: too many arguments for format|

This is line that is generating one of the warnings (line 122):

Code:

        fscanf( writePtr, "%d%[^0-9-]&d%d", &toolNumber, toolName, &toolQuanity, &toolCost );

This function takes multiple arguments. The first parameter is a file pointer, the second parameter is the format string, and then there should be one parameter for each of the format specifiers (%d). This error says the number of specifies does not match the number of parameters that follow. You have 3 specifiers (all ints %d) but you have 4 parameters (int*, C-string, int*, int*).

You may want to review the documentation for scanf() or fscanf().

Jim

Originally Posted by jimblumberg

This is line that is generating one of the warnings (line 122):

Code:

        fscanf( writePtr, "%d%[^0-9-]&d%d", &toolNumber, toolName, &toolQuanity, &toolCost );

This function takes multiple arguments. The first parameter is a file pointer, the second parameter is the format string, and then there should be one parameter for each of the format specifiers (%d). This error says the number of specifies does not match the number of parameters that follow. You have 3 specifiers (all ints %d) but you have 4 parameters (int*, C-string, int*, int*).

You may want to review the documentation for scanf() or fscanf().

Jim

I see my error, I put "

&d" instead of "%d"....thank you, that fixed the list tools function.

But I am still getting some strange behavior.

The Add Tool function is entering in 2 rows even if I only enter 1 row. For example, if I enter in "hammer 25 10", the program will write "1 hammer 25 10" to the file twice. And then, if I enter another tool, say a drill, it will delete one of the hammer entries, but put in 2 rows of the drill.

I went through the add tool code, but I don't see anything that would do this.

Thanks

Post your current code. It would also be helpful if you pointed out where your "Add Tool function" is located. Did you fix the item pointed out in post #3, there is more than just one place you are making this mistake.

Jim

You are still using feof() to control a loop. Look at line 97 in the above code. You are still not using the fscanf() on line 126 correctly.

Code:

        fscanf( writePtr, "%d%[^0-9-]%d%d", &toolNumber, toolName, &toolQuanity, &toolCost );

Count the number of format specifiers in your format string, you will only find 3, yet you have 4 variables that you are trying to fill. Where is the format specifier for your C-string toolName?

Please show a small sample of your data.

Jim

Originally Posted by jimblumberg

You are still using feof() to control a loop. Look at line 97 in the above code. You are still not using the fscanf() on line 126 correctly.

Code:

        fscanf( writePtr, "%d%[^0-9-]%d%d", &toolNumber, toolName, &toolQuanity, &toolCost );

Count the number of format specifiers in your format string, you will only find 3, yet you have 4 variables that you are trying to fill. Where is the format specifier for your C-string toolName?

Please show a small sample of your data.

Jim

Hi Jim,

I tried replacing feof() on line 97 with "while ( fgets(buf, sizeof(buf), readPtr) != NULL)" but that caused my file to remain empty(nothing was getting written to it).

Line 126...I looked up fscanf() and I think I am using it correctly. I have the file pointer, then the formatting(int, string, int, int) and then my 4 variables(int, string, int, int).

After 4 rows...I get this when I list all tools:

2 Drill 10 50
3 Wrench 50 12
4 Screwdriver 50 5
4 Screwdriver 50 5
4 Screwdriver 50 5

But the file actually contains this:

1 Hammer 100 10
2 Drill 10 50
3 Wrench 50 12
4 Screwdriver 50 5
4 Screwdriver 50 5

So something is still wrong...

thank you

Code:

#include <stdio.h> 

int main(void) { //  
   int i,qty;
   double cost;
   char name[40];
   FILE *fp;
   fp=fopen("test.txt", "r");
   
   while((fscanf(fp, "%d %s %d %lf",&i,name,&qty,&cost))>2) { 
      printf("%d  %s %d %.2f\n",i,name,qty,cost);   
   } 
   fclose(fp);
   printf("\n");
   return 0;
}

fgets() also works well for this.

I put in cost as a double - not sure if it should be or not.

Why are you trying to use fgets()? Using fread() would make more sense. Instead of this:

Code:

        /* copy all records from random-access file to text file */
        while ( !feof( readPtr ) )
        {
             fread( &hardware, sizeof( struct hardwareData ), 1, readPtr );

Something like:

Code:

        size_t numToRead = sizeof(struct hardwareData);
        while ( fread( &hardware, sizeof( numToRead ), 1, readPtr ) == numToRead )
        {
            /* write single record to text file */
             if ( hardware.recordNum != 0 )

Jim