Why cant scanf read white spaces?

Question

Why does scanf not read white spaces?

Also in my code if I use scanf first then fgets or scanf the second time after a few lines, as you can see in the code, then if I give an input that has a space like, "Hey How are u" then my code loops, why so?

I fixed it by just using fgets

while(1)
{
entry=&entry_var;
*entry=0;
printf("\n++++++++DFS CLIENT MENU++++++++");
printf("\n1-    ENTER THE COMMAND");
printf("\n2-    EXIT\n");
/*instance 1:if I use scanf here then whether i use scanf or fgets the
second time it loops in *entry==1 */
fgets (command, sizeof(command), stdin);
*entry=atoi(command);
printf("Entry: %d", *entry);
if(*entry==1)
{
    printf("\n--------COMMANDING ZONE--------");
    printf("\nInput the Function: ");
    //This is the second instance           
    fgets (command, sizeof(command), stdin);
    //scanf("%s",command);
    printf("\n%s",command);
    command_parse(command);
}
else if(*entry==2)
{
    break;
}
}

[mixing fgets and scanf](http://stackoverflow.com/questions/5918079/fgets-doesnt-work-after-scanf) — Barmar, Oct 24 '15 at 01:18
`scanf` is for reading and parsing tokens like numbers and words. Spaces are the separators between the tokens, it generally skips over them. — Barmar, Oct 24 '15 at 01:18
Thank you! I read the link that you posted, is there a way to empty this buffer? in the link it says scanf reads the string and leaves the \n in the buffer which causes the looping problem, so is there a command by which I can empty this buffer? — Anurag, Oct 24 '15 at 01:25
Use `fgets()` to read lines of data; use `sscanf()` when you want to parse the line of data. It has many advantages, including that it avoids the problems you're running into. — Jonathan Leffler, Oct 24 '15 at 01:57
@PC Luddite A weakness to `while (getchar() != '\n');` is that it is an infinite loop should `stdin` get closed. — chux - Reinstate Monica, Oct 24 '15 at 03:37

chux - Reinstate Monica · Answer 1 · 2015-10-24T18:49:25.433

Why cant scanf read white spaces?

This is a false question as scanf() does read white spaces.

scanf() reads from stdin and given various directives and specifiers, does its best to match them. Some specifiers cause scanf() to save data.

"%d" specifies scanf() to:
1- Read and discard all white-space.
2- Read and covert numeric text into an int, saving the result into i.
3- Continue step 2 until reading a non-numeric character, which is returned to stdin.
4- Return 1 if step 2 successful. Return 0 if step 2 only encountered non-numeric input. Else return EOF.

int i;
if (1 == scanf("%d", &i)) GoodToGo();

All scanf() format specifiers except "%c", "%n", "%[]", first read and discard leading white-space.

"%c" specifies scanf() to:
Read a char into c, including any whitespace character.
Return 1 or EOF.

char c;
if (1 == scanf("%c", &c)) GoodToGo();

scanf() and family details are beyond a simple answer here. Check on-line resources for details.

Better to use fgets() to read a line than scanf(any_format)

Why cant scanf read white spaces?

1 Answers1