未初始化的值是在调用不同函数时由堆分配创建的。

Question

守则如下：

Board* constructBoard(int dimension)
{
    //Allocate memory for board
    Board *board = malloc(sizeof(Board));
    if(!board)
    {
        return NULL;
    }
    //Allocate memory for matrix
    board->matrix = malloc(dimension * sizeof(int*));
    if(!board->matrix)
    {
        freeBoard(board);
        return NULL;
    }
    //Allocate memory for each row of matrix
    for(int row = 0; row < dimension; row++)
    {
        // Following line is line 29 from error below  <---------------------------
        board->matrix[row] = malloc(dimension * sizeof(int));  
        if(!board->matrix[row])
        {
            freeBoard(board);
            return NULL;
        }
        board->dimension = row +1;
    }
    board->value = 0;
    return board;
}

void printBoard(Board *board, char* delimiter)
{
    assert(board && "printBoard must get an initialized board");
    for(int i = 0; i < board->dimension; i++)
    {
        for (int j = 0; j < board->dimension; j++)
        {
            printf("%d%s", board->matrix[i][j], delimiter);
        }
        printf("\n");
    }
}

从main这样呼叫时：

Board *final = constructBoard(4);
printBoard(final, SEPARATOR);
freeBoard(final);

结果出现以下val差错率错误(请参阅上面代码中的注释中的错误行)：

==8450==  Uninitialised value was created by a heap allocation
==8450==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==8450==    by 0x401560: constructBoard (Board.c:29)
==8450==    by 0x400FAB: main (SudokuSolver.c:181)

Board的定义

typedef struct Board
{
    int** matrix;
    int dimension;
    unsigned int value;
} Board;

当我不向printBoard添加调用时，一切都很好。

1. 为什么只在使用printBoard时才得到错误？
2. 为什么当我得到错误时，它说它在constructBoard中

我已经阅读了前面的这些问题，但是我仍然没有解决它，因为我正确地分配了内存，并且确保循环只迭代有效的索引：

1. Uninitialised value was created by a stack allocation
2. Uninitialised value was created by a stack allocation - valgrind
3. Uninitialised value was created by a stack allocation

我使用以下标志进行了编译：

gcc -g -c -Wextra -Wall -Wvla -DNDEBUG -std=c99

Answer 1

malloc函数只分配内存，它不以任何方式初始化该内存。内存的内容不确定。

您可以在printBoard函数中打印此未初始化内存的内容，从而得到警告。

如果您想初始化内存，那么要么显式地执行它，要么使用calloc来分配和“清除”(零)内存(它等同于malloc，然后是memset)。