c - 麻烦取消对结构的双指针

Question

我似乎无法读取双指针指向的数据。它用于分配，因为我必须使用双指针。

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，您的调用void printPolyNode(const PolyNode* node)必须更改：

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

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

一定是

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)函数内部，您必须取消引用双指针，我的意思是：

• argTerm是指向指针的struct PolyTerm指针。
• *argTerm是一个指向struct PolyTerm

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;
}

经过

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。