c-重新定位第二个尺寸

Question

我正在使用为数组分配空间

int **pml=0;
int **tmp=(int **)realloc(pml, 100 * sizeof(*pml));
pml=tmp;

并尝试分配二维

  for ( i = 0; i < 100;i++){
       pml[i]=(int *)malloc(10 * sizeof ( int ));
       pml[i][0]=2; // for storing index
       pml[i][1]=10; // for realoc
  }

我试图实现的是：用户输入2个数字，第一个是索引，第二个是值，所以如果我输入3和5，数组应该看起来像

array{{2,10},{2,10},{2,10},{2,10,5}}

我用这个伏特加X=第一个数字，例如索引Y=值；

  if(pml[X][0]==pml[X][1]){
                pml[X][1]+=10;
                pml[X]=(int *)realloc(pml[X], pml[X][1] * sizeof ( int );}
                pml[X][pml[X][0]=X;
                pml[X][pml[0]]+=1;
           }

但随着输入量的增加，抛出分段故障Valgrind抛出此消息

==4270== Invalid read of size 8
==4270==    at 0x400873: main (in ../a.out)
==4270==  Address 0x5445f40 is 0 bytes after a block of size 2,400,000 alloc'd
==4270==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4270==    by 0x4C2CF1F: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4270==    by 0x400778: main (in /../a.out)
==4270== 
==4270== Invalid read of size 4
==4270==    at 0x400876: main (in /../a.out)
==4270==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==4270== 
==4270== 
==4270== Process terminating with default action of signal 11 (SIGSEGV)
==4270==  Access not within mapped region at address 0x0
==4270==    at 0x400876: main (in /h../a.out)
==4270==  If you believe this happened as a result of a stack
==4270==  overflow in your program's main thread (unlikely but
==4270==  possible), you can try to increase the size of the
==4270==  main thread stack using the --main-stacksize= flag.
==4270==  The main thread stack size used in this run was 8388608.
==4270== 
==4270== HEAP SUMMARY:
==4270==     in use at exit: 14,400,000 bytes in 300,001 blocks
==4270==   total heap usage: 300,001 allocs, 0 frees, 14,400,000 bytes allocated
==4270== 
==4270== LEAK SUMMARY:
==4270==    definitely lost: 0 bytes in 0 blocks
==4270==    indirectly lost: 0 bytes in 0 blocks
==4270==      possibly lost: 0 bytes in 0 blocks
==4270==    still reachable: 14,400,000 bytes in 300,001 blocks
==4270==         suppressed: 0 bytes in 0 blocks
==4270== Rerun with --leak-check=full to see details of leaked memory
==4270== 
==4270== For counts of detected and suppressed errors, rerun with: -v
==4270== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
Segmentation fault

这意味着一些realloc出现了错误，但我没有看到任何错误——我在哪里错误地重新分配了字段？

Answer 1

看起来您正在尝试创建一个动态数组或堆栈。你可以通过使用一个结构来极大地简化事情：

struct Stack {
    int capacity;
    int index;
    int *data;
};

然后，你想要100个（不确定为什么）。。。

struct Stack *pml = malloc(100 * sizeof(struct Stack));

然后初始化

for (int i = 0; i < 100; i++) {
    pml[i].capacity = 10;
    pml[i].index = 0;
    pml[i].data = malloc(10 * sizeof(int));
}

然后您可以使用功能设置数据

void Push(struct Stack *stack, int value) {
    // Check for reallocation
    if (stack->index == stack->capacity) {
        stack->capacity *= 2;  //Assumes capacity >= 1
        stack->data = realloc(stack->data, sizeof(int) * stack->capacity);
    }
    // Set the data
    stack->data[stack->index++] = value;
}

并称之为

Push(&pml[n], 234);   // Where n < 100, is the nth stack in the array

当然，你需要在某个时刻free()所有的东西。

（注意，您应该添加错误检查。）