我有一个创建函数，我想传递一个函数指针，但是我希望函数指针能够调用下面的任何一个函数，我遇到的问题是每个函数都返回不同的类型。但是当我传递函数指针时，我必须指定函数指针的返回类型。这是对的吗？ 我以为在 中使用 void 指针可以解决返回类型问题，但现在我无法调用函数指针。为了澄清，我想将populateMonsters或populateClassesTaken传递到create中，并能够在create内调用它们。
typedef struct node{
void * data;
struct node* next;
} node;
typedef struct MonsterAttacks{
unsigned int attackID;
char monsterName[41];
char attackLocation[41];
unsigned int numOfVictims;
}MonsterAttacks;
typedef struct ClassesTaken{
unsigned int classID;
char semester[41];
unsigned int year;
unsigned int numberOfUnits;
char grade[10];
}ClassesTaken;
unsigned int idM = 1;
MonsterAttacks * populateMonsters(){
MonsterAttacks *m = NULL;
m->attackID = idM;
printf("Enter the name for the Monster n");
scanf("%40s",m->monsterName);
puts("What is his/her attack location?");
scanf("%40s",m->attackLocation);
puts("What are the number of victims this monster has demolished?");
scanf("%ud", &m->numOfVictims);
//attackID is assigned and id when node is created
idM++;
return m;
}
unsigned int idC = 1;
ClassesTaken* populateClassesTaken(){
ClassesTaken *c = NULL;
c->classID = idC;
scanf("What semester was the class taken in? %40s",c->semester);
scanf("In what year? %ud", &c->year);
scanf("How many units was the class? %ud", &c->numberOfUnits);
scanf("What was your grade in the class? %9s", c->grade);
idC++;
return c;
}
node* create(node* next, void *fp)
{
node* new_node = (node*)malloc(sizeof(node));
if(new_node == NULL)
{
printf("Error creating a new node.n");
exit(0);
}
void *data = (*fp)();
}
int main(void)
{
node* tmp = NULL;
MonsterAttacks* (*fp)() = &populateMonsters;
create(tmp, *fp);
}
首先，不用说你不能像ClassesTaken *c = NULL; c->classID = idC;那样编写代码。如果你不明白为什么你不能，你需要回到学习指针的基础知识，如下所述： 将数据复制/扫描/读取到未初始化的指针时崩溃或"分段错误">
至于不同的功能 - 它们是不同的功能类型这一事实清楚地表明这种设计没有意义。如果要使用泛型函数指针，则需要定义统一的函数格式，例如void* func (void)。
不能将void*用作泛型函数指针。它仅用于指向对象的指针，而不是指向函数的指针。create(tmp, *fp);等代码，其中 fp 是函数指针，函数需要void*，不是有效的标准 C，不应编译，除非您使用的是非标准编译器扩展。
值得注意的是，切勿在 C 中声明带有空括号()的函数。这是一个过时的语言功能。(与C++不同，这很好，很鼓励。
populateMonsters()和populateClassesTaken()仍然存在问题。您希望用用户输入填充结构，但从不分配结构(无论是在堆上还是在堆栈上(。因此，您会出现分段错误。这是我没有类型定义的代码，包括，...
typedef void*(*myFunctionInterface)(void);
MonsterAttacks * populateMonsters (){
MonsterAttacks *m = (MonsterAttacks*)malloc(sizeof(MonsterAttacks));
if (m == NULL){
printf("Error creating MonsterAttacks");
exit (-1);
}
m->attackID = idM;
printf ("Enter the name for the Monster n");
scanf ("%40s", m->monsterName);
puts ("What is his/her attack location?");
scanf ("%40s", m->attackLocation);
puts ("What are the number of victims this monster has demolished?");
scanf ("%ud", &m->numOfVictims);
//attackID is assigned and id when node is created
idM++;
return m;
}
unsigned int idC = 1;
ClassesTaken * populateClassesTaken (){
ClassesTaken *c = (ClassesTaken*)malloc(sizeof(ClassesTaken));
if (c == NULL){
printf("Error creating ClassesTaken");
exit(-2);
}
c->classID = idC;
scanf ("What semester was the class taken in? %40s", c->semester);
scanf ("In what year? %ud", &c->year);
scanf ("How many units was the class? %ud", &c->numberOfUnits);
scanf ("What was your grade in the class? %9s", c->grade);
idC++;
return c;
}
node * create (node * next, void *(*fp) ()){
node *new_node = (node *) malloc (sizeof (node));
if (new_node == NULL)
{
printf ("Error creating a new node.n");
exit (-3);
}
void *data = fp();
new_node->data = data;
return new_node;
}
int main (void) {
node *tmp = NULL;
MonsterAttacks *(*fp_M) () = &populateMonsters;
ClassesTaken *(*fp_C) () = &populateClassesTaken;
create (tmp, (myFunctionInterface)fp_M);
}
在出现错误时返回 0 也不是一个好的样式。 0 通常表示一切正常。因此，我将退出值更改为一些不同的负数以区分错误
替换：
node* create(node* next, void *fp)
{
跟：
node* create(node* next, void* (*fp)())
{
和
create(tmp, *fp);
跟
create(tmp, (void*)fp); //[updated]
您的 populateMonsters(( 会导致分段错误。我用fputs("In populateMonstersn", stderr);替换了它的代码
它似乎有效：
$ ./a.out
在填充怪物中