Hi,
Why this code works:
and this one doesn't:Code:void main(){ char letter; char* str; printf("Enter char:"); fgets(&letter,2,stdin); printf("\n letter = %c",letter); }
ThanksCode:void main(){ char letter; char* str; printf("Enter char:"); fgets(&letter,1,stdin); // the change is 1 instead of 2 printf("\n letter = %c",letter); }
This doesn't work as well:
Code:void main(){ char letter; char* str; fputs("Enter char:",stdout); fgets(&letter,1,stdin); fputs(&letter, stdout); }
Last edited by DoK; 09-10-2017 at 07:52 AM.
You have not allocated any data space for "str".
And "letter" can only contain one letter.Code:char str[256];
Also we usually don't use fgets() to just get one char. We use getchar() instead, and putchar() to display it. Plus "letter" should be defined as an int, not a char.
> Why this code works:
> char letter;
> fgets(&letter,2,stdin);
Only through pure dumb luck does this "work". Change things around a bit, and it can soon "not work".
fgets() ALWAYS appends a \0 to whatever string it stores. So in this case, the \0 ends up overwriting someone else's memory.
It's also time to stop using void main as well.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Originally Posted by Salem
Thank you very much!
Thanks
Actually it is still not working :/
This is the new code:
thanks for the helpCode:#include <stdio.h> #include <stdlib.h> #include <string.h> void Ex1(){ char letter; char* str; fputs("Enter char: ",stdout); letter = getchar(); // it just skip this i think putchar(letter); // It doesn't print anything even if I do fflush(stdin); } void Ex2(){ puts("Ex2"); } int main(){ char choice; while(1){ fputs("#Please select the exercise (1-5, 0 to exit): ",stdout); choice = getchar(); switch (choice) { case '0': puts("Good bye"); return 0; case '1': Ex1(); break; case '2': Ex2(); break; } } return 0; }
Last edited by DoK; 09-10-2017 at 09:00 AM.
If you type in
1\n
Then main() will read '1' and Ex1() will read '\n'.
> It doesn't print anything even if I do fflush(stdin)
Because fflush() doesn't work on input streams.
If you want to clean up the input stream, then see the FAQ
FAQ > Flush the input buffer - Cprogramming.com
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Thanks again!
Is it legit if add this function:
?Code:void clear_stdin(){ int c; while((c = getchar()) != '\n' && c != EOF); } void Ex1(){ char letter; char* str; clear_stdin(); fputs("Enter char: ", stdout); letter = getchar(); putchar(letter); }
Looks good.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
You are the man
