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C中矩阵的分段故障(Segmentation fault in matrix in C)

 我试图在C中创建一个矩阵并有一些输入值，但我不知道为什么它会给我一个“分段错误”。 这是我的代码：  
#include <stdio.h> 
#include <stdlib.h>

int main() {
    int i;
    int j;
    int **a;
    a = malloc(5 * sizeof(int));
    for (i = 0; i < 5; i++) {
      a[i] = malloc(4 * sizeof(int));
    }
    for (i = 0; i < 5; i++) {
      for (j = 0; j < 4; j++) {
        scanf("%d", (a[i][j]));
      }
    }
    return 0;
}

I've tried to create a matrix in C and have some input value, but I don't know why it throws me a "segmentation error". This is my code: 
#include <stdio.h> 
#include <stdlib.h>

int main() {
    int i;
    int j;
    int **a;
    a = malloc(5 * sizeof(int));
    for (i = 0; i < 5; i++) {
      a[i] = malloc(4 * sizeof(int));
    }
    for (i = 0; i < 5; i++) {
      for (j = 0; j < 4; j++) {
        scanf("%d", (a[i][j]));
      }
    }
    return 0;
}

原文：

更新时间：2022-03-02 16:03

最满意答案

 对于您的特定情况，这应该工作：  
SELECT p.event_id, p.user_id
FROM public."point" p JOIN
     public."user" u
     ON p.user_id = u.id 
WHERE u.email = 'test@gmail.com';
 
 通常，在JOIN和IN之间切换时，需要注意重复。 所以一般的解决方案是：  
SELECT p.event_id, p.user_id
FROM public."point" p JOIN
     (SELECT DISTINCT u.id
      FROM public."user" u
      WHERE u.email = 'test@gmail.com'
     ) u
     ON p.user_id = u.id ;
 
 但id可能在user已经是唯一的。 

For your particular case, this should work: 
SELECT p.event_id, p.user_id
FROM public."point" p JOIN
     public."user" u
     ON p.user_id = u.id 
WHERE u.email = 'test@gmail.com';
 
In general, when switching between JOIN and IN, you need to be careful about duplicates. So the general solution would be: 
SELECT p.event_id, p.user_id
FROM public."point" p JOIN
     (SELECT DISTINCT u.id
      FROM public."user" u
      WHERE u.email = 'test@gmail.com'
     ) u
     ON p.user_id = u.id ;
 
But the id is probably already unique in user.

C中矩阵的分段故障(Segmentation fault in matrix in C)

最满意答案

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