指针是一个“未声明的标识符”

Question

这是代码：

// Simulate genetic inheritance of blood type

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

// Each person has two parents and two alleles
typedef struct person
{
    struct person *parents[2];
    char alleles[2];
} person;

const int GENERATIONS = 3;
const int INDENT_LENGTH = 4;

person *create_family(int generations);
void print_family(person *p, int generation);
void free_family(person *p);
char random_allele();

int main(void)
{
    // Seed random number generator
    srand(time(0));

    // Create a new family with three generations
    person *p = create_family(GENERATIONS);

    // Print family tree of blood types
    print_family(p, 0);

    // Free memory
    free_family(p);
}

// Create a new individual with `generations`
person *create_family(int generations)
{
    // TODO: Allocate memory for new person
    person *person = malloc(sizeof(person));
    if (person == NULL)
    {
        return NULL;
    }

    // If there are still generations left to create
    if (generations > 1)
    {
        // Create two new parents for current person by recursively calling create_family
        person *parent0 = create_family(generations - 1);
        person *parent1 = create_family(generations - 1);

        // TODO: Set parent pointers for current person
        person->parent[0] = parent0;
        person->parent[1] = parent1;

        // TODO: Randomly assign current person's alleles based on the alleles of their parents
        if (rand() % 2 == 0)
        {
            person->alleles[0] = person->parent[0]->alleles[0];
        }
        else
        {
            person->alleles[0] = person->parent[0]->alleles[1];
        }

        if (rand() % 2 == 0)
        {
            person->alleles[1] = person->parent[1]->alleles[0];
        }
        else
        {
            person->alleles[1] = person->parent[1]->alleles[1];
        }
    }

    // If there are no generations left to create
    else
    {
        // TODO: Set parent pointers to NULL
        person->parent[0] = NULL;
        person->parent[1] = NULL;

        // TODO: Randomly assign alleles
        person->alleles[0] = random_allele();
        person->alleles[1] = random_allele();
    }

    // TODO: Return newly created person
    return person;
    return NULL;
}

// Free `p` and all ancestors of `p`.
void free_family(person *p)
{
    // TODO: Handle base case
    if (p->parent[0] == NULL)
    {
        free(p);
        return;
    }

    // TODO: Free parents recursively
    free_family(p->parent[0]);
    free_family(p->parent[1]);

    // TODO: Free child
    free(p);
}

// Print each family member and their alleles.
void print_family(person *p, int generation)
{
    // Handle base case
    if (p == NULL)
    {
        return;
    }

    // Print indentation
    for (int i = 0; i < generation * INDENT_LENGTH; i++)
    {
        printf(" ");
    }

    // Print person
    if (generation == 0)
    {
        printf("Child (Generation %i): blood type %c%c\n", generation, p->alleles[0], p->alleles[1]);
    }
    else if (generation == 1)
    {
        printf("Parent (Generation %i): blood type %c%c\n", generation, p->alleles[0], p->alleles[1]);
    }
    else
    {
        for (int i = 0; i < generation - 2; i++)
        {
            printf("Great-");
        }
        printf("Grandparent (Generation %i): blood type %c%c\n", generation, p->alleles[0], p->alleles[1]);
    }

    // Print parents of current generation
    print_family(p->parents[0], generation + 1);
    print_family(p->parents[1], generation + 1);
}

// Randomly chooses a blood type allele.
char random_allele()
{
    int r = rand() % 3;
    if (r == 0)
    {
        return 'A';
    }
    else if (r == 1)
    {
        return 'B';
    }
    else
    {
        return 'O';
    }
}

显然错误出在 create_family 函数的 if 子句中：

    if (generations > 1)
    {
        // Create two new parents for current person by recursively calling create_family
        person *parent0 = create_family(generations - 1);
        person *parent1 = create_family(generations - 1);
    }

编译时出现的错误：

inheritance.c:52:17: error: use of undeclared identifier 'parent0'
        person *parent0 = create_family(generations - 1);
                ^

我尝试将指针的名称更改为与“person0”不同的名称，但仍然无法解决任何问题。我不明白为什么错误是“未声明的标识符”，我认为从这个意义上说，代码是正确的，并且创建指向这样的人的指针应该不是问题。在整个代码中没有像这样调用其他指针/元素。

Answer 1

您在以

person

开头的行上定义了一个名为

person *person

的变量。因此，您有一个名称完全相同的变量和类型，并且编译器对您编写

person *parent0

时的含义感到困惑：它认为您想要将 person 变量

parent0

乘

。

我建议您的类型名称以大写字母开头以避免这种情况。

Answer 2

person *person

不是最好的主意。之后

person

被解释为变量

person

，而不是类型。