c - 取消引用结构体的双指针时出现问题

Question

我似乎无法读取双指针指向的数据。这是为了我必须使用双指针的分配。

出现以下错误:

Error: Access violation reading location. 

这是代码:

struct Fraction {

        int num, denom;<br>
};
struct PolyTerm {

        struct Fraction coeff;
        int exponent;v
};
struct PolyNode {

    struct PolyTerm** dataPtr;
    struct PolyNode* next;
};

void printPolyTerm(struct PolyTerm** argTerm) { // this function works fine><br>

        printFraction(&(argTerm->coeff));       //also works fine
        printf(" X^%d", argTerm->expo);
        return;
}
void printPolyNode(const PolyNode* node) {  //NOT WORKING<br>

        struct PolyTermPS** ppTerm = node->dataPtr;
        struct PolyTermPS* pTerm = *ppTerm;
        printPolyTerm(pTerm);
        return;
}

Answer 1

函数 void printPolyTerm(struct PolyTerm** argTerm) 接受双指针，因此，来自 void printPolyNode(const PolyNode* node) 的调用必须更改:

void printPolyNode(const PolyNode* node) {  //NOT WORKING<br>

    struct PolyTermPS** ppTerm = node->dataPtr;
    struct PolyTermPS* pTerm = *ppTerm;
    printPolyTerm(pTerm);
    return;
}

必须是

void printPolyNode(const PolyNode* node) {  //NOT WORKING<br>

    struct PolyTerm** ppTerm = node->dataPtr;
    struct PolyTerm* pTerm = *ppTerm;
    printPolyTerm(&pTerm);
    return;
}

现在，在 void printPolyTerm(struct PolyTerm** argTerm) 函数中，您必须取消引用双指针，我的意思是:

• argTerm 是指向 struct PolyTerm 指针的指针。
• *argTerm 是指向 struct PolyTerm 的指针

所以，你必须更换

void printPolyTerm(struct PolyTerm** argTerm) { // this function works fine><br>

    printFraction(&(argTerm->coeff));       //also works fine
    printf(" X^%d", argTerm->expo);
    return;
}

由

void printPolyTerm(struct PolyTerm** argTerm) { // this function works fine><br>

    printFraction(&((*argTerm)->coeff));       //also works fine
    printf(" X^%d", (*argTerm)->exponent);
    return;
}

另一种情况之所以有效，只是因为你太幸运了。