c - "undefined variable"警告，但变量已在所有进程中定义

Question

编辑:发布的最新代码，直到最后一个警告...警告指出在第 97 行“recvbuffer”(在 MPI_Send 中)未定义...但是我在之前的所有进程中定义了 recvbuffer[totalnums]这点。当我到达代码的合并排序部分时，为什么程序不保留我定义的recvbuffer数组变量？

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <math.h>
#include <mpi.h>
#define TAG 25


int compare(const void *a, const void *b) {                     /* Comparison function for qsort */
    int var1, var2, ret;
    var1 = *(const int *)a;
    var2 = *(const int *)b;
    if (var1 == var2) {
        ret = 0;
    }
    else {
        ret = (var1 < var2) ? -1 : 1;
    }
    return ret;
}



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

    int rank, process;                              /* Variable declarations */

    MPI_Init(&argc, &argv);                             /* Initialize MPI */
    MPI_Comm_size(MPI_COMM_WORLD, &process);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    int size, origsize, h, i, j, k, p, q, r, s, v, x, z, chunk;         /* Variable declarations */
    int totalnums;                                  /* Variable declarations */

    if (rank != 0) {                                /* Receive totalnums value from process 0 for all processes */
        MPI_Recv(&totalnums, 1, MPI_INT, 0, TAG, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
        int recvbuffer[totalnums];                      /* Create recvbuffer array for all processes except root */
        qsort(recvbuffer, chunk, sizeof(int), compare);
    }

    if (rank == 0) {

        FILE *infilename;                           /* Initialize input file variable */

        infilename = fopen(argv[1], "r");                   /* Read input file */

        if (infilename == 0) {                          /* Check whether read-in file exists */
            printf("File not found.\n");
            return 1;
        }

        fscanf(infilename, "%d", &size);                    /* Obtain total number of items in file */

        totalnums = size;

        while (totalnums % process != 0) {                  /* Obtain total number of spots to allocate in array */
            totalnums += 1;
        }


        int A[totalnums];                           /* Declare array size */

        for (i = 0; i<size; i++) {                      /* Create array A[] from file using process 0 until end of file reached*/
            fscanf(infilename, "%d", &A[i]);
        }

        origsize = size;                            /* Store original value for total numbers in file */

        for (x = size; x < totalnums; x++) {                    /* Fill in empty spots at end of array with INT_MAX numbers */
            A[x] = INT_MAX;
        }

        fclose(infilename);                         /* Close the incoming file */

        MPI_Bcast(&origsize, 1, MPI_INT, 0, MPI_COMM_WORLD);            /* Broadcast origsize and send totalnums to all processes */
        for (h = 1; h < process; h++) {
            MPI_Send(&totalnums, 1, MPI_INT, h, TAG, MPI_COMM_WORLD);
        }

        int recvbuffer[totalnums];                      /* Create recvbuffer array in process 0 */

        chunk = totalnums/process;                      /* Calculate chunk size for each process */

        MPI_Scatter(A, chunk, MPI_INT, recvbuffer, chunk, MPI_INT, 0, MPI_COMM_WORLD);                  /* Send select chunk to each process */
        qsort(recvbuffer, chunk, sizeof(int), compare);             /* Perform sort on each chunk in individual processes */
    }

    int step, mergebuffer[totalnums], combinedbuffer[totalnums];            /* Create step and mergebuffer array variables */

    printf("stage 2 complete.\n");

    for (z = 0; z <= ((process-1)/2); z++) {                    /* Start mergesort */
        for (step = 1; step < process; step = 2*step) {
            if (rank % (2*(2 << z)*step) != 0) {
                MPI_Send(recvbuffer, (2 << z)*chunk, MPI_INT, rank-(step*(2 << z)), TAG, MPI_COMM_WORLD);       /* Send elements to partner process */
                break;
            }
            else {
                MPI_Recv(mergebuffer, (2 << z)*chunk, MPI_INT, rank+(step*(2 << z)), TAG, MPI_COMM_WORLD, MPI_STATUS_IGNORE);   /* Receive elements from partner process and store in mergebuffer */
                p = 0;
                q = 0;
                r = 0;
                while (p != (2 << z)*chunk && q != (2 << z)*chunk) {                    /* Start combining and sorting buffers */
                    if (recvbuffer[p] > mergebuffer[q] || q == (2 << z)*chunk) {
                        combinedbuffer[r] = recvbuffer[p];
                        r++;
                        p++;
                    }
                    else if (recvbuffer[p] <= mergebuffer[q] || p == (2 << z)*chunk) {
                        combinedbuffer[r] = mergebuffer[q];
                        r++;
                        q++;
                    }
                }
                v = 0;
                while (v != (2 << z)*chunk) {                           /* Copy combinedbuffer into recvbuffer to start next iteration */
                    recvbuffer[v] = combinedbuffer[v];
                }
            }
        }
        printf("get to here?\n");
    }

    if (rank == 0) {

        FILE *outfilename;                          /* Initialize output file variable */
        outfilename = fopen(argv[2], "w");                  /* Create output file */

        fprintf(outfilename, "Sorted array of %d elements:\n", origsize);   /* Print first line of output file */
        s = 0;
        for (j = 0; j < (totalnums/10); j++) {                  /* Create multiple rows of 10 numbers per row */
            for (k = 0; k < 10; k++) {                  /* Cycle 10 times */
                if (recvbuffer[s] != INT_MAX) {             /* Print next number to file until first INT_MAX entry reached */
                    fprintf(outfilename, "%d  ", recvbuffer[s]);
                }
                s++;                        /* Increase value to proceed through entire list */
            }
            fprintf(outfilename, "\n\n");                   /* Print two returns at end of each 10 number row */
        }
        fclose(outfilename);                            /* Close the outgoing file */

    printf("Stage 4 complete.\n");
    }

    MPI_Finalize();                                 /* Finalize MPI */

    printf("\n");

    return 0;

}

Answer 1

回答您关于 MPI_Bcast 有问题的评论。您正在调用此函数三次。

int MPI_Bcast(void *buffer, int count, MPI_Datatype datatype, int root, MPI_Comm comm)

第一个参数采用缓冲区的地址。您的三个通话中的最后一个是这个

MPI_Bcast(recvbuffer, totalnums, MPI_INT, 0, MPI_COMM_WORLD);

这看起来相当不错，因为您传递了缓冲区(以及隐式的其地址)及其大小。但你的前两个电话是

MPI_Bcast(origsize, 1, MPI_INT, 0, MPI_COMM_WORLD);
MPI_Bcast(totalnums, 1, MPI_INT, 0, MPI_COMM_WORLD);

在这两种情况下，您都传递了包含 1 个元素的缓冲区，但没有传递缓冲区地址。虽然我不完全遵循您的代码，但我建议尝试以下操作:

MPI_Bcast(&origsize, 1, MPI_INT, 0, MPI_COMM_WORLD);
MPI_Bcast(&totalnums, 1, MPI_INT, 0, MPI_COMM_WORLD);

注意添加的 & 来指示地址。在第一个语句中，您传递了一个数组，因此它的地址在语句中是隐式的，但对于单个整数则不然。