Help reading from a file into a structure array

iblink · #1 28-Oct-2009, 17:02

Hello. I am trying to read info from a file into an array of a created structure. After running the program on visual studio 2008, it gives me no syntax error but this dialog box appears "debug assertion failed". Can anyone look at my code and tell me the problem.. Thanks in advance.

CPP / C++ / C Code:

#include<stdio.h>

//void display();
int main()
{
	struct persalary
	{
		int month;
		long salary;
	};
	struct employee
	{
		int empnr;
		char name[12];
		struct persalary salaries[3];
		long total;
		float average;
	}person[3];
	int i=0;

	FILE *emp_file;
	emp_file = fopen("emp.txt","r");

	do{
	fscanf(emp_file,"%d %s %d %ld %d %ld %d %ld", &person[i].empnr, person[i].name, &person[i].salaries[0].month,
			&person[i].salaries[0].salary,&person[i].salaries[1].month, &person[i].salaries[1].salary,
			&person[i].salaries[2].month, &person[i].salaries[2].salary);
	i++;
	}while(feof(emp_file)==0);
	fclose(emp_file);

	return 0;
}

The content of the file is as follows:

Code:

121  Alex      2   300000  4  400000  12   750000     		                    
234  Andy     3   250000  6  800000   7   475000  		                                  
456  Mart     4    750000  5  880000  10   660000      
875  Steven  2   950000  4  660000   9   775000

fakepoo · #2 28-Oct-2009, 17:24

You are trying to read 4 students into an array that can only hold 3.

davekw7x · #3 28-Oct-2009, 17:30

You declare an array of three structs ant then you try to store data for more than three.

Try something like the following to see how it goes:

CPP / C++ / C Code:

    do {
        int n = 
        fscanf(emp_file, "%d %s %d %ld %d %ld %d %ld", &person[i].empnr,
               person[i].name, &person[i].salaries[0].month,
               &person[i].salaries[0].salary, &person[i].salaries[1].month,
               &person[i].salaries[1].salary, &person[i].salaries[2].month,
               &person[i].salaries[2].salary);
        printf("i = %d, n = %d\n", i, n);
        i++;
    } while (feof(emp_file) == 0);

If you increase you dimension to more than four, it shouldn't crash the way that it did, but I'm thinking that you should see why your loop is not right.

For example, I get the following:

Code:

i = 0, n = 8
i = 1, n = 8
i = 2, n = 8
i = 3, n = 8
i = 4, n = -1

With four lines in the file, it goes through the loop five times. (The eof flag is not set until after it tries to read past the end of the file.)

That topic (improper use of eof as a loop control) has been covered numerous times, but I know it's hard to believe that it simply doesn't work the way that you want it to without seeing it for yourself.

If get past the crash (by increasing the size of the array) but you still can't find how to make the loop work properly, let us know, and maybe someone can give some more clues.

Bottom line: Always (yes, always test the result of a read operation to see that the proper number of items was read!

Regards,

Dave

iblink · #4 28-Oct-2009, 17:40

Thank You very much.. Works great after increasing the size of the array person[] by 1. I do understand well how reading the file works, thanks to your example.

davekw7x · #5 28-Oct-2009, 18:12

Quote:

Originally Posted by iblink

...I do understand well how reading the file works....

So did you change your loop so that it does not attempt to store five things from your four-line file? I mean, even if it happens not to actually crash the program, you need to read exactly what the file has. Neither more nor less.

Regards,

Dave

iblink · #6 28-Oct-2009, 18:18

exactly what i do.. works fine.. thx

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Help reading from a file into a structure array

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