accumulate.c

/**
a simple example of std::accumulate implemented in C
*/

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


#define ARRSIZE(X) (sizeof(X) / sizeof(X[0]))


#define ACCUMULATE(RET, FIRST, LAST, INIT, SUM_CB)      \
    do {                                                \
        RET = INIT;                                     \
        while (FIRST != LAST){                          \
            RET = SUM_CB(RET, *FIRST);                  \
            FIRST++;                                    \
        }                                               \
    } while(0);


struct str_t
{
    char data[512];
};



struct str_t sumStr(struct str_t a, struct str_t b)
{
    struct str_t ret = {0};
    strcat(ret.data, a.data);
    strcat(ret.data, "--");
    strcat(ret.data, b.data);
    return ret;
}


struct A { int a, b, c; };

struct A sumA(struct A a, struct A b) {
    struct A ret ;
    ret.a = a.a + b.a;
    ret.b = a.b + b.b;
    ret.c = a.c + b.c;
    return ret;
}


int main()
{
    unsigned long i;

    struct A sumvec[10];
    struct str_t sumstr[10];
    memset(sumstr, 0, sizeof(sumstr));

    for(i=0; i < ARRSIZE(sumvec); i++) {
        sumvec[i].a = i;
        sumvec[i].b = i+1;
        sumvec[i].c = i+2;
        snprintf(sumstr[i].data, sizeof(sumstr[i].data), "%d", i);
    }

    for(i=0; i < ARRSIZE(sumvec); i++) {
        printf("[%d][%d][%d]\r\n", sumvec[i].a ,sumvec[i].b,sumvec[i].c);
    }


    struct A ret = {sumvec[0].a, sumvec[0].b, sumvec[0].c};
    struct A* pBegin = &sumvec[1];
    struct A* pEnd = &sumvec[ARRSIZE(sumvec)];

    ACCUMULATE(ret, pBegin, pEnd,  ret, sumA)

    printf("SUM: [%d][%d][%d]\r\n", ret.a, ret.b, ret.c);


    struct str_t retstr;
    strcat(retstr.data, sumstr[0].data);

    struct str_t *pBegs = &sumstr[1];
    struct str_t *pEnds = &sumstr[ARRSIZE(sumstr)];

    ACCUMULATE(retstr, pBegs, pEnds, retstr, sumStr);

    printf("SUM STR: [%s]\r\n", retstr.data);
    return 0;
}