Find Unique Characters in a File

Question

I have a file with 450,000+ rows of entries. Each entry is about 7 characters in length. What I want to know is the unique characters of this file.

For instance, if my f

Answer 1

A C solution. Admittedly it is not the fastest to code solution in the world. But since it is already coded and can be cut and pasted, I think it counts as "fast to implement" for the poster :) I didn't actually see any C solutions so I wanted to post one for the pure sadistic pleasure :)

#include

#define CHARSINSET 256
#define FILENAME "location.txt"

char buf[CHARSINSET + 1];

char *getUniqueCharacters(int *charactersInFile) {
    int x;
    char *bufptr = buf;
    for (x = 0; x< CHARSINSET;x++) {
        if (charactersInFile[x] > 0)
            *bufptr++ = (char)x;
    }
    bufptr = '\0';
    return buf;
}

int main() {
    FILE *fp;
    char c;
    int *charactersInFile = calloc(sizeof(int), CHARSINSET);
    if (NULL == (fp = fopen(FILENAME, "rt"))) {
        printf ("File not found.\n");
        return 1;
    }
    while(1) {
        c = getc(fp);
        if (c == EOF) {
            break;
        }
        if (c != '\n' && c != '\r')
            charactersInFile[c]++;
    }

    fclose(fp);
    printf("Unique characters: {%s}\n", getUniqueCharacters(charactersInFile));
    return 0;
}