c - How to allocate memory while using typedef?

Question

I have a code segment which goes something like this

typedef struct node* node_t;

struct node{
int value;
node_t link;
};

......
......
......

//now I want to allocate memory somewhere else in the program.
node_t x;
x=(node_t) malloc(sizeof *x);

Could you please tell me if the above statement is proper? Eclipse shows this warning

warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration]
../tree.c:22:9:
warning: incompatible implicit declaration of built-in function ‘malloc’    

Can someone explain in detail about situations like this? What is actually wrong with this. I would really appreciate if you could list all the possible ways in which I can allocate memory in this program? Thank you in advance..

Answer 1

为了使用malloc，您需要包含<stdlib.h>. 此外，分配内存，如

node_t x = malloc(sizeof node_t);

您不能将内存分配给堆栈变量，而只能分配给指针。并且永远不要转换回分配的类型，作为malloc返回void*，这不需要显式转换。

Answer 2

You need an

#include <stdlib.h>

before you use malloc. You apparently declared the function wrong in your source. Never declare C standard library functions. Just include the headers that declare them.

Answer 3

Could you please tell me if the above statement is proper?

No, it isn't: you're casting the return value of malloc() and you're missing the <stdlib.h> header.

Answer 4

您收到警告是因为您没有malloc范围内的声明；您需要包含stdlib.h头文件：

#include <stdlib.h>

你也应该放弃演员表。这不是必需的，并且在其他编译器下会抑制您尝试将int值分配给指针类型的诊断。

请不要将指针隐藏在 typedef 后面。这几乎总是一个坏主意。