CODEWITHSUNDEEP
c
country_dev
country_dev

Reputation: 605

scanning until EOF in c

I am writing a decryption program and I need to scan in an unknown number of strings and decode each string as it is entered. The program must end once it reaches EOF.

I am having difficulty getting the program to end. when I scan in the first char in the string in my while loop condition statement, it is doing this but when I scan in the actual string bellow the condition statement the string is missing the first char. Should I scan in the first char and then somehow put that char at the beginning of the string?

How do I properly test for EOF in my situation? 

#include <stdio.h>
#include<string.h>

int main(void)
{
    int i;
    char code[300];

    while(scanf("%c", &code[0])!=EOF)
    {
        scanf("%s", code);

        for(i=0; i<strlen(code); i++)
        {
            decrypt message one char at a time
        }
        printf("\n");
    }
    return 0;
}

Upvotes: 3

Views: 25251

Answers (3)

Keith Thompson
Keith Thompson

Reputation: 263237

Using scanf at all is a bad idea for this particular problem.

while(scanf("%c", &code[0])!=EOF)

This scanf call reads a single character. Just use getchar().

scanf("%s", code);

for(i=0; i<strlen(code); i++)
{
    decrypt message one char at a time
}

The scanf call can read arbitrarily many characters (after skipping whitespace; are you sure you want to skip whitespace?). That means that if there are too many characters to be read from stdin, you have a buffer overflow, one that you can't avoid unless you have complete control over what appears on stdin.

You then loop over the code array, calling strlen() for each character you process. Since strlen() generally has to scan from the beginning of the array to the terminating '\0', this is inefficient. If you need to traverse the characters of a string, either call strlen() once and save the value, or look for the terminating '\0' character.

But you're just processing one character at a time, so just read one character at a time:

while ((c = getchar()) != EOF) {
    /* process a character */
}

Don't worry about reading one character at a time being inefficient; buffering will take care of that.

Upvotes: 0

Jim Balter
Jim Balter

Reputation: 16406

while (scanf("%s", code) == 1)
{
    // no need for second scanf call
    ...

Upvotes: 4

Edward Clements
Edward Clements

Reputation: 5132

while (scanf("%c", &code[0]) == 1)
{   scanf("%s", &code[1]);
    ...

Upvotes: 0

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