输入来自Kernighan和Ritchie的例子

Question

In section 1.5.2 of the 2nd ed. K&R introduce getchar() and putchar() and give an example of character counting, then line counting, and others throughout the chapter.

Here is the character counting program

#include <stdio.h>
main() {

long nc;

nc = 0;
while (getchar() != EOF)
    ++nc;
printf("%ld\n",nc);
}

where should the input come from? typing into the terminal command window and hitting enter worked for the file copying program but not for this. I am using XCode for Mac.

It seems like the easiest way would be to read a text file with pathway "pathway/folder/read.txt" but I am having trouble with that as well.

Answer 1

From the interactive command line, press ctrl-D after a newline, or ctrl-D twice not after newline, to terminate the input. Then the program will see EOF and show you the results.

To pass a file by path, and avoid the interactive part, use the < redirection operator of the shell, ./count_characters < path/to/file.txt .

Answer 2

Standard C input functions only start processing what you type in when you press the Enter key IOW.Every key you press adds a character to the system buffer (shell).Then when the line is complete (ie, you press Enter), these characters are moved to C standard buffer. getchar() reads the first character in the buffer, which also removes it from the buffer.Each successive call to getchar() reads and removes the next char, and so on. If you don't read every character that you had typed into the keyboard buffer, but instead enter another line of text, then the next call to getchar() after that will continue reading the characters left over from the previous line; you will usually witness this as the program blowing past your second input. BTW, the newline from the Enter key is also a character and is also stored in the keyboard buffer, so if you have new input to read in you first need to clear out the keyboard buffer.