警告：＆＃x2018; dot_prod＆＃x2019;可以在此功能[-wmaybe-initialization]中使用非专业化。

Question

我一直在修改此代码，似乎无法使其正常工作。当我运行错误文件时，会生成后，我会得到警告

dotp.c:39:11: warning: ‘dot_prod’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   39 |   #pragma omp parallel for reduction(+: dot_prod) num_threads(num_td)
      |           ^~~

，我不明白我如何使dot_prod概念化或是否可以解决错误，任何人都可以帮助我修复它吗？太感谢了。

#include <omp.h>
#include <stdio.h>
#include <time.h>
#include <stdlib.h>
#include <math.h>


int main(int argc, char **argv){
        
    int exe_mode, num_td, vec_size;
    
    
    sscanf(argv[0], "%d", &exe_mode);
    sscanf(argv[1], "%d", &num_td);
    sscanf(argv[2], "%d", &vec_size);

    srand(1);

    int a[vec_size];
    int b[vec_size];
    int dot_prod,i;
    
    double start = omp_get_wtime();
    
    //initializing the vectors
    for( i = 0; i < vec_size; i++){ 
        a[i] = (int) (rand() % vec_size - vec_size/2);
        b[i] = (int) (rand() % vec_size - vec_size/2);
    }
    
    //Sequential execution
    if (exe_mode == 1){
        for( i = 0; i<vec_size;i++){
            dot_prod += a[i] * b[i];
        }
    }   
    //Parallel execution
    if (exe_mode == 2){
        #pragma omp parallel for reduction(+: dot_prod) num_threads(num_td)
        for(i=0; i<vec_size;i++){
            dot_prod += a[i] * b[i];
        }
    }
    //Parallel execution with vectorization
    if (exe_mode == 3){
        #pragma omp simd reduction(+: dot_prod)
        for( i=0; i<vec_size;i++){
            dot_prod += a[i] * b[i];
        }
    double runtime = omp_get_wtime()-start;
    printf("%.4e\t%i\n", runtime ,dot_prod);    
    }
    
    
    
    return 0;
}

/**void dotproduct(int exe_mode, int num_td, int vec_size){
    
    srand(1);
    
    int a[vec_size];
    int b[vec_size];
    int dot_prod;
    
    //initializing the vectors
    for(int i = 0; i < vec_size; i++){ 
        a[i] = (int) (rand() % vec_size - vec_size/2);
        b[i] = (int) (rand() % vec_size - vec_size/2);
    }
    
    //Sequential execution
    if (exe_mode == 1){
        for(int i=0; i<vec_size;i++){
            dot_prod += a[i] * b[i];
        }
    }   
    //Parallel execution
    if (exe_mode == 2){
        #pragma omp parallel for num_threads(num_td)
        for(int i=0; i<vec_size;i++){
            dot_prod += a[i] * b[i];
        }
    }
    //Parallel execution with vectorization
    if (exe_mode == 3){
        #pragma omp parallel for simd num_threads(num_td)
        for(int i=0; i<vec_size;i++){
            dot_prod += a[i] * b[i];
        }
    double runtime = omp_get_wtime();   
    printf("%.4e\t%i\n", runtime ,dot_prod);    
    }
}**/**strong text**

Answer 1

将您的dot_prod声明更改为：

int dot_prod = 0;
int i;

Answer 2

dot_prod +=（数字表达式）是未定义的行为，如果您没有初始化dot_prod。

您初始化dot_prod以初始化任何其他int varible的方式相同;通过将其设置为一些预定的值，例如零。

int dot_prod = 0;

没有该初始分配， dot_prod可以在声明时包含任何int值。您的C编译器仅需要为您的变量分配一些内存；不需要在此处放置一些明智的初始值。你必须自己做。