Guidelines and Common Errors

Building test

• You’ll lose all the points in MP0 if compilation of char_count failed.
• Invalid filenames (eg. Makefile.txt, char_count.exe, etc), wrong file hierarchy, or absence of Makefile grants 0 point.

Standard error test

• The stderr output should print exactly error\n only when INPUT_FILE doesn’t exist, or you’ll get 0 point. Those writing to stdout grant no points.

Feature test, aka. small/large input test

• Your program should handle both INPUT_FILE and stdin. Otherwise both small and large tests are marked failing.
• The extreme test can be a single line exceeding 1GB. Those reading data with getline(), gets()/fgets() will suffer from buffer overflow. The spec mentioned the line size can be arbitrarily large. Thus, it’s not a good idea to read the whole line with a fixed length buffer.
• Any printable and space characters can be included in CHARSET and every characters are counted without exception. Therefore, those filtering out spaces will result in wrong answer.
• Every line is guranteed to have trailing \n, and thus it can be treated as the end-of-line mark. Some incorrectly handles \n and EOF cases, causing the program prints additional lines at the end of output. In this case it will fail both small/large input tests.

Example Implementation

Makefile

.PHONY: clean all

all: char_count

clean:
	rm -f char_count

char_count: char_count.c
	gcc -o char_count char_count.c -Wall

Source code (char_count.c)

#include <stdio.h>

int main(int argc, char* argv[])
{
    /* Init CHARSET lookup table. */
    unsigned char charSet[128] = {};
    for (int i = 0; argv[1][i] != '\0'; i++) {
        charSet[(int)argv[1][i]] = 1;
    }

    /* Read from stdin by default. */
    FILE* fileInput = stdin;

    /* Read from file if argc is 3. */
    if (argc == 3) {
        fileInput = fopen(argv[2], "r");
    }

    /* Print error message if fopen failed. */
    if (fileInput == NULL) {
        fprintf(stderr, "error\n");
        return 0;
    }

    int c;
    int count = 0;
    while ((c = fgetc(fileInput)) != EOF) {
        if (c == '\n') {
            /* Print number of matched char. */
            printf("%d\n", count);
            count = 0;
        } else if (charSet[c] == 1) {
            /* Add one to counter if in CHARSET */
            count++;
        }
    }
    return 0;
}