Thread: First C program.. please help

Hi,

Just a short comment: If you want read in data from the command line (as a program argument), then you must define your Main func. as follows:

int main (int argc, char **argv) {

.... the rest of the code...


return 1;

}

argv is an array of strings (it stores all the info). argc is the number of elements in argv.

These are standard names. If they're not defined then your program will be unable to read command line options.

Also check out the getopt(), getopt_long() and getopt_long_only() functions (at least getopt() is available in the standard C library, but in GNU's version you'll find all of them.). These are helpful, if there are many command line opts to read...etc.)

And last but not least: if you want to fetch the data from stdin, I would recommend scanf() instead of getchar(). It is much more robust.

Thats's it. Good luck! -

Just one more thing:

Why do you use #define? Although, it is valid, you should use local variables instead whenever it's possible.

>> addr = getchar();

This is invalid. You have to declare addr first like this.

char addr;

Also, getchar will read only one character at a time! This not suitable for reading in strings. Use scanf() or fscanf() or sscanf()

If you want to create a file, then you'll need stream manipulation functions as well (such as fopen(), freopen()..etc.)

I suggest you to download the documentation of GNU C Library. This is a help file which contains detailed info about all the standard functions, data types, macros, header files and lot of other stuff.

You can get it from this site:

http://www.bloodshed.net/dev/doc/bin/libc.zip

An online version is also available:

http://www.gnu.org/manual/glibc-2.2..../libc_toc.html

Well, that's all for now. - Be good! -











range = "addr.START";

>>Also, getchar will read only one character at a time! This not suitable for reading in strings. Use scanf() or fscanf() or scanf()
Or perhaps you should investigate fgets(), if you don't want to build in functions that allow buffer overflows.

Hi!

Yes, fgets is better, however I'm not sure what does he mean by "taking input from the command line". If he wants to type in something then scanf() is good, else of course fgets is the right choice.

getline() is another alternative.

Bye!

Originally posted by Bill 101
Yes, fgets is better, however I'm not sure what does he mean by "taking input from the command line". If he wants to type in something then scanf() is good, else of course fgets is the right choice.

getline() is another alternative.

fgets() will get from the keyboard as well, and is safer than scanf().

getline() ? That isn't a standard function.

Code:

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

int main( int argc , char *argv[] )
{
    int cnt_main;
    FILE *fPtr;

    if ( argc == 1 )
        printf( "Usage : IP addres e.g <190.20.0>" );
    else{

       if ( (fPtr = fopen( "network.txt" ,"w" )) != NULL ){
          for ( cnt_main = 0; cnt_main <= 255; cnt_main++ )
              fprintf(fPtr, "%s.%d\n", argv[1], cnt_main );

       fclose( fPtr );
       }
       else
          printf( "Error could not create file" );
    }

        return 0;
}

Originally posted by Hammer
>>Also, getchar will read only one character at a time! This not suitable for reading in strings. .....

other method ??

scanf ("%[^\n]", variable);

this can help you input the string that you have entered.
this code could help you when the user enter the input, user enter the name and hit enter. when the io detect the "enter (or '\n') it will save the whole words before the \n into the variable....

eg :

| enter your name > beely name of the words

then the variable is saved as --> beely name of the words.


=== compare this !

scanf ("%s",variable);

then the variable contains : beely
that mean, when it detect a space after a word. the others will discard saving into the variable.

Originally posted by beely
other method ??

scanf ("%[^\n]", variable);

<snip>

As I already posted, use fgets() to get a line of data.