在没有EOF时获取文本

Question

Here's my code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define N 256

int main(int argc, const char * argv[]) {

    char testo[N];
    int i;
    printf("PER TERMINARE L'INSERIMENTO PREMERE CTRL+Z oppure CTRL+D \n");
    for(i=0;i<N;i++)
    {
        scanf("%c",&testo[i]);
        /* if(testo[i]=='h' && testo[i-1]=='c')
        {
            i--;
            testo[i]='k';
        }
        if(testo[i]==testo[i-1])
        {
            i--;
        } */
        if(testo[i]==EOF)
        {
            break;
        }
    }

    puts(testo);

    return 0;
}

When the code in /* ... */ is compiled, I can't stop the insert of text with EOF, but when the code is built and run as shown here, the EOF works.

Does anyone have any idea what the problem is?

Answer 1

You're testing for EOF incorrectly. With scanf() , you need to look at the return value. In fact, with almost all input functions, you need to test, if not capture and test, the return value.

Superficially, you need:

for (i = 0; i < N; i++)
{
    if (scanf("%c", &testo[i]) == EOF)
        break;
    …
}

However, in general, you should check that scanf() made as many successful conversions as you requested, so it is better to write:

for (i = 0; i < N; i++)
{
    if (scanf("%c", &testo[i]) != 1)
        break;
    …
}

In this example, it really won't matter. If you were reading numeric data, though, it would matter. The user might type Z instead of a number, and scanf() would return 0, not EOF.

Answer 2

To detect EOF , check the result of scanf()

if scanf("%c",&testo[i]) == EOF) break;

---

Note: testo[] may not be null character terminated. To print as a string, insure it is.

char testo[N];
int i;

// for(i=0;i<N;i++) {
for(i=0;i<(N-1);i++) {
  if (scanf("%c",&testo[i]) == EOF) break;
}

testo[i] = '\0';  // add
puts(testo);

Answer 3

To stop at end of file, check the return value from scanf :

scanf returns the number of inputs correctly parsed. In your case, %c reads a byte from the stream correctly as long as end of file has not been reached. if (scanf("%c",&testo[i]) != 1) break; will do.

Yet using scanf to read one byte at a time from the input stream is overkill. The idiomatic way to do this in C is using the getchar() or the getc() function. The return value must be stored in an int variable and has special value EOF upon end of file.

You should also make the array 1 byte longer and store a null byte at the end to make it a C string, as expected by puts .

Here is a modified version of your program:

int main(int argc, const char *argv[]) {
    char testo[N+1];
    int i;

    printf("PER TERMINARE L'INSERIMENTO PREMERE CTRL+Z oppure CTRL+D\n");

    for (i = 0; i < N; i++) {
        int c = getchar();
        if (c == EOF)
            break;
        testo[i] = c;
        /* ... further processing ... */
    }
    testo[i] = '\0';

    puts(testo);
    return 0;
}