TYPEDEF需要结构声明 [英] typedef required in struct declaration

问题描述

我试图创建结构元素的数组，如下所示：

I'm trying to create an array of struct elements, as shown below:

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

struct termstr{
double coeff;
double exp;
};

int main(){

termstr* lptr = malloc(sizeof(termstr)*5);

return 0;
}

当我编译这个，我得到的错误如下：

When i compile this, i get errors as follows:

term.c: In function ‘main’:
term.c:11:1: error: unknown type name ‘termstr’
term.c:11:31: error: ‘termstr’ undeclared (first use in this function)

然而，当我改变我的code到下面，它编译像往常一样：

However, when i change my code to the following, it compiles as usual:

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

typedef struct termstr{
double coeff;
double exp;
}term;

int main(){

term* lptr = malloc(sizeof(term)*5);

return 0;
}

我添加的typedef（含类型名称的术语），改变了结构的名称termstr和我分配与长期记忆*为指针的类型。

I've added typedef (with type name as term), changed the name of struct to termstr and am allocating memory with term* as the type of pointer.

时的typedef总是需要这样的情况，即用于创建结构数组？如果不是，为什么是第一个code给人错误？是的typedef还需要创建和使用结构的一个实例？

Is typedef always required for such a situation i.e. for creating arrays of structs? If not, why was the first code giving errors? Is typedef also required to create and use a single instance of a struct?

推荐答案

第一种类型是不工作，因为你已经忘了结构关键字之前 termstr 。你的数据类型为结构termstr 而不仅仅是 termstr 。当你的typedef ，所得到的名称用作结构termstr 的别名。

First type is not working because you have forgot struct keyword before termstr. Your data type is struct termstr but not just termstr. When you typedef, the resulting name is used as an alias for struct termstr.

即使你不需要这么做。使用的typedef 更好：

Even you don't need to do that. Using typedef is better:

顺便说一句，不要忘记释放内存：

By the way don't forget to free the memory:

使用的typedef？

您的工作code应该是：

Your working code should be:

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

struct termstr{
  double coeff;
  double exp;
};

int main(){

struct termstr* lptr = malloc(sizeof(struct termstr)*5);
free(lptr);
return 0;
}

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