Why does fputc() skips every other character

Question

I have a small program in C which starts with a menu which is implemented inside a function with a do{switch{case 1....}while loop

When case 1 validates it calls another function where a while loop takes getchar() values and write them into a file using fputc(). The problem is that it skips every other character.

Is there a trick around it?

So that my do{} while menu with its switch case can coexist with an isolated function that hosts my while loop and it's fputc() method?

Here a simplified version of the code.....

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

int menu();
int v1();

int main(void) {
  menu();
  return 0;
}

int menu() {
  int opt;
  do {
    printf("\t 1] v1 \n");
    switch (opt) {
      case 1:
        v1();
    }
    scanf("%i", &opt);
  } while (opt != 100);
  return 0;
}

int v1() {
  FILE *fd;
  char target[10] = "v1.json";
  fd = fopen(target, "at");
  if (fd == NULL) {
    printf("Error");
  }
  int c;
  while ((c = getchar()) != EOF && (c = getchar()) != '\n') {
    fputc(c, fd);
  }
  fclose(fd);
  return 0;
}

Andres Sanchez Muñoz "it skips every other character." --> Do you consider the enter key a character? — chux - Reinstate Monica, Aug 06 '18 at 18:38
Possible duplicate of [scanf() leaves the newline char in the buffer](https://stackoverflow.com/questions/5240789/scanf-leaves-the-new-line-char-in-the-buffer). Similarly with `getchar()`. — Weather Vane, Aug 06 '18 at 18:41
Considering the number of problems this causes, I am amazed that C has no standard function to input a single character, such as one keystroke from the console. MS has `getch()`and `kbhit()`. They may have got a lot of other things wrong, but I like those functions. Sadly they can't be used in standard C. — Weather Vane, Aug 06 '18 at 18:49
@AndresSanchezMuñoz Please edit that into the text of your question, so we can read it with proper formatting. (Did you know that you can edit your question? The tiny gray word "edit" below the tags is a button. Yes, really.) — zwol, Aug 06 '18 at 18:54
@WeatherVane this may help you outside of MS. https://stackoverflow.com/questions/29612201/implicit-declaration-of-function-getch/29612473#29612473 — Deanie, Aug 06 '18 at 19:13
Posting your sample input, output seen and output expected is very useful. — chux - Reinstate Monica, Aug 06 '18 at 19:16
The `while` loop calls `getchar` twice, but `fputc` only once, for each iteration of the loop. — user3386109, Aug 06 '18 at 19:16
@Deanie your link only illustrates my point: obtaining a single input "when-entered" requires a lot of stuff. It is such a common ocurrence and there are so many questions here. I believe the C standard is deficient, although there may be good reasons *why* the committee decided. — Weather Vane, Aug 06 '18 at 19:16
`while ((c = getchar()) != EOF && (c = getchar()) != '\n') {` --> `while ((c = getchar()) != EOF && c != '\n') {` — chux - Reinstate Monica, Aug 06 '18 at 19:16
Aside. Well _declared_ functions in C should not omit `void`. `int menu(); int v1();` --> `int menu(void); int v1(void);` - else they lack a signature check. — chux - Reinstate Monica, Aug 06 '18 at 19:18
Absolutely. I aplied the corrections @chux it works fine now . Thanks! — Andres Sanchez Muñoz, Aug 06 '18 at 19:26

score 3 · Answer 1 · answered Aug 06 '18 at 22:25

In the line

while ((c = getchar()) != EOF && (c = getchar()) != '\n') { ... }

you're reading in two characters from stdin, not one--because you're calling getchar() twice.

In order to fix that, since you already assigned the read char to the variable c, just use the variable in the second comparison, rather than calling the function once more:

while ((c = getchar()) != EOF && c != '\n') { ... }

Why does fputc() skips every other character

1 Answers1