Fgets() keeps skipping first character

Question

This is part of a larger program to emulate the cat command in unix. Right now trying to take input and send it to stdout:

char in[1000];
int c = 0; 
while ((c = getchar()) != EOF)
 {
   fgets(in,1000,stdin);
   fputs(in, stdout);
 }

This sends output to stdout, but in every case it skips the first letter. For instance, if I type the word Computer

I get back:

omputer

Wershba

That is because the first character gets stored in getchar() – Felicific

You want while (fgets(in,1000,stdin)) and don't forget to remove the fgets in the body of the while loop. – Evans

Do instead while (fgets(...) != NULL) – Normalcy

Answer 1

Your problem is all about eating.

c = getchar()

This line, as many I/O operations in C consume your buffer. Meaning that when you have say 0123456789 after your getchar() you're left with 123456789 in your buffer.

What you want to do is use the same functions to control the input and to store it, so something like getting rid of the getchar() should do the trick :

while (fgets(in,1000,stdin) != NULL)
 {
   fputs(in, stdout);
 }

And there you have it !

Roundshouldered

Answer 2

There is an ungetc function that allows to return character to a stream. It is not standard C function, but implemented in Unix-like systems and by Visual Studio CRT:

while ((c = getchar()) != EOF)
{
    ungetc(c, stdin);
    fgets(in, 1000, stdin);
    fputs(in, stdout);
}

But as other answerers note, cleaner way to do that is to use fgets() directly:

while (fgets(in, sizeof(in), stdin) != NULL)

The third option is to save first character directly to a string:

while ((c = getchar()) != EOF)
{
    in[0] = c;
    fgets(in + 1, 999, stdin);
    fputs(in, stdout);
}

Pentheus

I did not now about ungetc(), +1 for that – Roundshouldered

Answer 3

It's not skipping anything you are consuming it with getchar().

Upon successful completion, fgets() returns the string in. If the stream is at end-of-file, the end-of-file indicator for the stream shall be set and fgets() shall return a NULL pointer.

Change this

while ((c = getchar()) != EOF)

to

while (fgets(in, sizeof(in), stdin) != NULL)  

Trepang

Answer 4

This will work too:

char in[1000];
while ((in[0] = (char)getchar()) != EOF)
 {
   fgets(in+1,999,stdin);
   fputs(in, stdout);
 }

Swig

If getchar() returns 255, then with signed char, in[0] would have the value of -1. This may match EOF even though end-of-file did not occur. – Nonintervention

How do you make getchar() return 255? – Swig

Many ways. Example: 1) FILE * f= fopen("test.txt", "w"); fputc(255, f); fclose(f): Now pipe that file into you program "a.bin < text.txt" 2) On many PC keyboard using standard IO: <Alt> key down, <number pad 2> <number pad 5> <number pad 5> <Alt> key up. 3) getchar(), by spec, returns an int in the range of unsigned char or EOF. It does not specify it will not return 255 - so code should be prepared to handle all 257 different values. – Nonintervention