Thread: Is there a convenient way to write ints & floats to a file in binary mode?

I'm converting them to strings using sprintf then using fwrite but I'm getting strange errors so I figure there must be something simpler.

Do you want them to appear in binary form? If so, why are you converting them to strings using sprintf?

Well, would there be any other way to write them then using fwrite?

If you wanted them in the file in binary form, you would use fwrite only, without sprintf.

Doing fwrite(&i, sizeof(int), 1, fp) and fwrite(&fl, sizeof(float), 1, fp), I get even stranger errors.

You're going to have to be way way way way more specific (as in, code and actual errors).

Code:

class data
{
public:
	char last[31], first[36];
	float salary;
	int yrhired;
	void display(void);
	void modify(void);
	data(void);
}employee[20];



void save(void){
	int savecount = 0;
	FILE *fp;
	char endline[2];
	endline[0] = '\n';
	endline[1] = '\r';
	fp = fopen("company.db", "wb");
	while (savecount < 20){
		fwrite("Last: ", 1, 6, fp);
		fwrite(employee[savecount].last, 1, 30, fp);
		fwrite(endline, 1, 2, fp);
		fwrite("First and Middle: ", 1, 18, fp);
		fwrite(employee[savecount].first, 1, 35, fp);
		fwrite(endline, 1, 2, fp);
		fwrite("Salary: ", 1, 8, fp);
		fwrite(&(employee[savecount].salary), sizeof(float), 1, fp);
		fwrite(endline, 1, 2, fp);
		fwrite("Year hired: ", 1, 12, fp);
		fwrite(&(employee[savecount].yrhired), sizeof(int), 1, fp);
		fwrite(endline, 1, 2, fp);

		savecount++;
	}

void retrieve(void){
	char character;
	FILE *fp;
	fp = fopen("company.db", "rb");
	while ((character = fgetc(fp)) != EOF){
		printf("%c", character);
	}
	fclose(fp);
	prompt();

}

The above code is what I believe is relevant. Using this, whenever an employee object is "retrieved" (i.e. printed on the screen) regardless of the input, the ouput is this

Code:

Last:
First and Middle:
Salary:      ?(upside-down question mark)
Year hired:

When I use sprintf, if I edit say the third employee, in the salary and year hired place for employees 4 through 20 there are numbers following the data that shouldn't be there (e.g. instead of -1.00000 it's -1.0000 9).

Why do you expect fgetc to be able to read binary data? (Hint: It won't.) You use fread to read binary data back in. Or, if fgetc is what you want, then you don't want to use fwrite towrite binary data in the first place.

The main problem isn't the reading (which I have now fixed), it's the fact that the writing is all screwy. Take a look at the attachment.

I have no idea where you got the data for last and first, so who knows what's there. If you can read numeric data in notepad, you did it wrong.

Code:

void save(void){
	int savecount = 0;
	FILE *fp;
	char newline[1];
	newline[0] = '\n';
	fp = fopen("company.db", "wb");
	while (savecount < 20){
		strcpy (ints,"     ");
		strcpy (floats, "         ");
		fwrite("Last: ", 1, 6, fp);
		fputs(employee[savecount].last, fp);
		fwrite(newline, 1, 1, fp);
		fwrite("First and Middle: ", 1, 18, fp);
		fputs(employee[savecount].first, fp);
		fwrite(newline, 1, 1, fp);
		fwrite("Salary: ", 1, 8, fp);
		snprintf(floats, 10, "%.2f", employee[savecount].salary);
		fputs(floats, fp);
		fwrite(newline, 1, 1, fp);
		fwrite("Year hired: ", 1, 12, fp);
		sprintf(ints, "%d", employee[savecount].yrhired);
		fputs(ints, fp);
		fwrite(newline, 1, 1, fp);

		savecount++;
	}
	fclose (fp);
	prompt();
}

Why does this produce garbage at the end of the salary?

I could make my code better but I'm okay with how it is. I just want to know why the code I posted produces garbage at the end of salary and I'm good to go.