wc.reducer.c

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/** \file wc.reducer.c
    \brief Example for KMR shell command pipeline.  It is a reducer
    for word count. */

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

/** Maximum line length. */
#define LINELEN 32767

/** Maximum key-value string length. */
#define KEYLEN 32767

/** Reducer main routine.
    Read stdin and reduce. Write result to stdout.  */

int
main(int argc, char *argv[])
{
    char line[LINELEN], prevkey[KEYLEN];
    char *key = NULL;
    long sum = 0;

    memset(prevkey, 0, sizeof(prevkey));
    while (fgets(line, sizeof(line), stdin) != NULL) {
        char *cp = line;
        int len = (int)strlen(line);
        long count;

        // chomp
        if (cp[len-1] == '\n') {
            cp[len-1] = '\0';
        }
        key = line;
        cp = strchr(line, ' ');
        if (cp == NULL) {
            // No value field.
            //printf("skip line\n");
            continue;
        }
        *cp++ = '\0';

        count = 0;
        while (cp - line < len) {
            long val;
            char *endptr = NULL;
            val = strtol(cp, &endptr, 10);
            if (val == 0 && cp == endptr) {
                // no value field.
                break;
            }
            count += val;
            cp = endptr;
        }

        if (strlen(prevkey) == 0) {
            // No saved key.
            memset(prevkey, sizeof(prevkey), 0);
            // save key.
            strncpy(prevkey, key, sizeof(prevkey)-1);
            sum = count;
            continue;
        }
        if (strcmp(prevkey, key) != 0) {
            // key changed.
            printf("%s %ld\n", prevkey, sum);
            memset(prevkey, sizeof(prevkey), 0);
            // save 'current' key.
            strncpy(prevkey, key, sizeof(prevkey)-1);
            sum = count;
        } else {
            // continue with same key. Add count.
            sum += count;
        }
    }
    if (strlen(prevkey) > 0) {
        printf("%s %ld\n", prevkey, sum);
    }
    fflush(stdout);
    return 0;
}