CODEWITHSUNDEEP
cnewlinescanf
user3043146
user3043146

Reputation: 1

Requiring scanf to recognise no input

im very new to C programming, and i am looking for the simplest possible solution to getting scanf to recognise no input, by that i mean pressing the enter key with nothing typed and it knowing nothing has been entered and returning to the main menu. Iv looked about on here and i found a similar problem but scanf was taking an integer value, whereas i require a string for a filename. My code is:

    FILE *Fpacket;
    char filename[20];

    puts("Please declare a name for the file");   // request filename  
    scanf("%s", filename);    // store text in filename string

I have tried a combination of fgets, getchar and afew others but i just cant get it to take the newline character as input. I am aware scanf ignores preceding whitespace, any help greatly appreciated!

Thanks

Upvotes: 0

Views: 886

Answers (2)

chux
chux

Reputation: 153447

There is no solution using %s in scanf("%s", filename) as the format specifier consumes whitespace, including \n before attempting to fill filename. scanf() will not return until non-whitespace (or EOF or IO Error) occurs.

Much better to use fgets()/sscanf()

char buf[MAXPATH + 2];
if (fgets(buf, sizeof buf, stdin) == NULL) handle_EOF_IOError();
if (buf[0] == '\n')
  handle_OnlyEnterKeyPressed();
else 
  sscanf(buf, "%s", filename);

Upvotes: 2

SantanuXCowBoy
SantanuXCowBoy

Reputation: 1

If you want to take a Newline(Enter) character from the keyboard as input, then you need to use another key to terminate the string //press Esc to terminate the string.

int main() {
char filename[20];
char ch;
int i;
i=0;
while ((filename[i] = std::cin.get()) != 27 && i<20) {
i++;
}
return 0;
}

If you press enter on your keyboard, it will take it as character and store it on filename[i], the while loop will never terminate until you press Esc or i<20

Upvotes: -1

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