Question

今天我尝试编写代码，但我无法弄清楚我做错了什么

我怀疑的是，我以某种方式分配了这个矩阵有些错误，我得到了Segmentation fault，这意味着我试图访问一些不存在的内存位置。属于我。

以下是该计划：

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

#define ROW 2
#define COL 5

int main(void){
    int **table;

    /* allocate memory for the pointers to rows */
    table = malloc(ROW * sizeof(*table));

    if(table){
        /* dynamic number of elements */
        for (int i = 0 ; i < ROW ; i++){
            /* Memory allocation for the number of items in each ROW */
            *(table + i) = malloc( COL * sizeof(*table[i]) );
        }
    }else{
        printf("Malloc error\n");
        exit(1);
    }

    printf("Type 10 Numbers: ");
    for (int i = 0 ; i < ROW ; i++){
        for (int j = 0 ; j < COL ; j++){
            if((scanf("%d",&*(*(table+i)+j))) != 1){
                printf("Error, scanf\n");
                exit(2);
            }
        }
    }

    printf("The numbers are:\n");
    for (int i = 0 ; i < ROW ; i++){
        for (int j = 0 ; j < COL ; j++){
            printf("%d ",*(*(table+i)+j));
        }
        printf("\n");
    }

    for (int i = 0 ; i < COL ; i++){
        if ( *(table + i) != NULL ) {
            free ( *(table + i) );
            *(table + i) = NULL;
        }
    }

    if(table){
        free(table);
    }
    printf("\n");
}

以下是Valgrind所说的内容：

==4842== Command: ./program
==4842== 
Type 10 Numbers: 10 20 30 40 50 10 20 30 40 50
The numbers are:
10 20 30 40 50 
10 20 30 40 50 
==4842== Invalid read of size 8
==4842==    at 0x400886: main (program.c:43)
==4842==  Address 0x51fc050 is 0 bytes after a block of size 16 alloc'd
==4842==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4842==    by 0x40071F: main (program.c:11)
==4842== 

==4842== 
==4842== HEAP SUMMARY:
==4842==     in use at exit: 0 bytes in 0 blocks
==4842==   total heap usage: 3 allocs, 3 frees, 56 bytes allocated
==4842== 
==4842== All heap blocks were freed -- no leaks are possible
==4842== 
==4842== For counts of detected and suppressed errors, rerun with: -v
==4842== ERROR SUMMARY: 3 errors from 1 contexts (suppressed: 0 from 0)

所以问题似乎在这里：

table = malloc(ROW * sizeof(*table));

但我不确定。究竟我在这里做错了什么？

Answer 1

您使用valgrind很好，但您还没有正确理解输出。

== 4842 ==读取大小为8

== 4842 ==在0x400886：main（program.c：43）

== 4842 ==地址0x51fc050在大小为16的块之后是0字节＆＃39; d

== 4842 ==在0x4C2AB80：malloc（在/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so中）

== 4842 == by 0x40071F：main（program.c：11）

错误在第43行，即此行：

if ( *(table + i) != NULL ) {

它正在读取您在第11行分配的内存之外的地址。这并不一定意味着第11行有任何问题。

问题是你已经迭代了行数而不是第42行中的列数：

for (int i = 0 ; i < COL ; i++){

这应该是：

for (int i = 0 ; i < ROW ; i++){

动态分配2D矩阵的分段故障

1 个答案: