arguments.......questions!!

erwfili · 10-31-2009, 08:16 AM

i am trying to understand a c code for the arguments in C but i get a bit confused....i will be pleased if you answer me some questions for the code....
1. why in function myRead the programmer uses two files as a parameter of the function???i only have one file to open....
2.while(argc==1) the parameters of the function is myread(stdin,stdout) but in else is myread(fp,stdout)...why this is different????
3. if i want to read from a file...can i always use the function myread as a standard function for read from a file???

Code:

#include <stdio.h>

void myRead(FILE *, FILE *);

int main(int argc, char *argv[]) {
	FILE *fp;
    	if(argc == 1)
		myRead(stdin, stdout);
    	else
		while(--argc > 0)
			if((fp = fopen(*++argv, "r")) == NULL) {
				printf("Can't open file: %s\n", *argv);
				return 1;
			}
			else {
				myRead(fp, stdout);
			
				fclose(fp);
			}
    	return 0;
}
    
void myRead(FILE *fpe, FILE *fps) {
	int c;
    	while((c = getc(fpe)) != EOF)
		putc(c, fps);
}

i will be thankfull if you help me cause i am not standing computer science...but i have a midterm on wedsday in c..

Nylex · 10-31-2009, 08:25 AM

Quote:

Originally Posted by erwfili

1. why in function myRead the programmer uses two files as a parameter of the function???i only have one file to open....

Do you understand what the function does? If you do, it should be clear why there are two arguments.

Quote:

2.while(argc==1) the parameters of the function is myread(stdin,stdout) but in else is myread(fp,stdout)...why this is different????

Do you know about the arguments to main (i.e. argc and argv)? If not, learn about them and you should be able to work out what's going on.

erwfili · 10-31-2009, 08:31 AM

i know what does the arguments means but i get a bit confused...thanks for your help....

pixellany · 10-31-2009, 08:33 AM

For starters, where did you get this code?

The function is defined such that it gets characters from one file and the sends them (put) to another file. That is why there are two arguments.

When the function is called, you have to tell it the source and destination. In one case, it is simply "stdin" and "stdout" (which I assume are defined in stdio.h). In the other case, "fp" is used instead of "stdin". Which option gets used is determined by the number of arguments sent to main().

For context, please tell us where you are in your studies--eg is this your first class in C?

Nylex · 10-31-2009, 08:38 AM

Quote:

Originally Posted by erwfili

i know what does the arguments means but i get a bit confused...thanks for your help....

You need to say what you get confused about, because how else will we know?

Quote:

Originally Posted by pixellany

For starters, where did you get this code?

The function is defined such that it gets characters from one file and the sends them "put" to another file. That is why there are two arguments.

When the function is called, you have to tell it the source and destination. In one case, it is simply "stdin" and "stdout" (which I assume are defined in stdio.h). In the other case, "fp" is used instead of "stdin". Which option gets used is determined by the number of arguments sent to main().

I suppose you and I have different approaches to "teaching". I prefer to gauge what they know and get them to think a bit

.

pixellany · 10-31-2009, 08:43 AM

Quote:

Originally Posted by Nylex

I suppose you and I have different approaches to "teaching". I prefer to gauge what they know and get them to think a bit

.

I'm making no attempt at teaching. If I were, there would be a very different dialog.

I make quick judgement calls about the appropriate response to a question. I this case, it was obviously homework, but there was also evidence of prior effort. I posted what seemed to me to be the best way to get OP going in the right direction......YMMV

erwfili · 10-31-2009, 08:47 AM

Code:

if(argc == 1)
		myRead(stdin, stdout);

this means that if there is not any file in command line the only elements excists is the name of the programme e.g. ./programme ,why we read from a file....while the file does not excists....??

pixellany · 10-31-2009, 08:53 AM

You lost me......That code fragment says that if the argument count is 1, then execute "MyRead" using stdin and stdout. In that case it is not necessarily reading from a file, but from whatever stdin has be defined to be----ie typically the keyboard.

As I requested previously, please tell us more about the context of your questions.

erwfili · 10-31-2009, 08:57 AM

ok i think i am in a good way....thanks a lot for your help and for the time that you dedicated to me!!!i hope to make it up!!

pixellany · 11-01-2009, 08:02 AM

Moved: This thread is more suitable in <Programming> and has been moved accordingly to help your thread/question get the exposure it deserves.