parameters of fopen

EDIT: I don't know why the code is all on a single line. Even after I edit the post to correct the format, the code still reverts to a single line. Blah.Hi folks.Below is sample code from a book that I am working through. Why does the program work when there is no "" around the mode?if ((fopen(filename, r) == NULL)) doesn't work, so why does the below program work?Thanks in advance.

Code:

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/* Demonstrates the fopen() function. */#include #include int main( void ){  FILE *fp;  char ch, filename[40], mode[4];    while (1)    {        /* Input filename and mode. */        printf("\nEnter a filename: ");        gets(filename);        printf("\nEnter a mode (max 3 characters): ");        gets(mode);        /* Try to open the file. */        if ( (fp = fopen( filename, mode )) != NULL )        {            printf("\nSuccessful opening %s in mode %s.\n",                    filename, mode);            fclose(fp);            puts("Enter x to exit, any other to continue.");            if ( (ch = getc(stdin)) == 'x')                break;            else                continue;        }        else        {            fprintf(stderr, "\nError opening file %s in mode %s.\n",                    filename, mode);            puts("Enter x to exit, any other to try again.");            if ( (ch = getc(stdin)) == 'x')                break;            else                continue;        }    }    return 0;}

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Hi folks.Below is sample code from a book that I am working through. Why does the program work when there is no "" around the mode?

if ((fopen(filename, r) == NULL)) doesn't work, so why does the below program work? Thanks in advance.

Code:

---


/* Demonstrates the fopen() function. */
#include <stdlib.h>
#include <stdio.h>

int main( void )
{
  FILE *fp;
  char ch, filename[40], mode[4];

    while (1)
    {

        /* Input filename and mode. */

        printf("\nEnter a filename: ");
        gets(filename);
        printf("\nEnter a mode (max 3 characters): ");
        gets(mode);

        /* Try to open the file. */

        if ( (fp = fopen( filename, mode )) != NULL )
        {
            printf("\nSuccessful opening %s in mode %s.\n",
                    filename, mode);
            fclose(fp);
            puts("Enter x to exit, any other to continue.");
            if ( (ch = getc(stdin)) == 'x')
                break;
            else
                continue;
        }
        else
        {
            fprintf(stderr, "\nError opening file %s in mode %s.\n",
                    filename, mode);
            puts("Enter x to exit, any other to try again.");
            if ( (ch = getc(stdin)) == 'x')
                break;
            else
                continue;
        }
    }
    return 0;
}

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First of all, please fix your code formatting. Edit: you just fixed it right before my post. :)

Second of all, I would chuck that book and find a better one if I were you.

gets() is bad. There is no safe way to use it.

Assigning the return value from getchar()/getc() to a char variable is (generally) bad. getchar() and getc() return an unsigned character converted to an int, so you can't reliably test for EOF if you save it to a char (which this code doesn't do properly either).

At least it doesn't have "void main" or other travesties like that.

To answer your question, though, mode is a string variable (technically it's an array of char).

Thanks christop!