如何为函数中的结构分配内存？ [英] How to allocate memory to a struct in a function ?

问题描述

我在这个函数中有一个函数create_system我想将内存分配给一个名为c_array的数组，它的tipe是一个指向struct Activity的指针。

i得到我尝试分配的方式记忆错了！我尝试了所有的东西，我搜索了整个谷歌以这种方式分配：

活动*（（* sys） - > c_array）= malloc（num_challenges * sizeof（活动））; 

但我得到了以下错误：

预期'）'之前' - >'令牌

我在这里做错了任何帮助！提前谢谢



我尝试过：

 typedef struct SRoomSystem 
 {
 Activity * c_array; 
 
} RoomSystem; 
 int num_challenges = 6; //这只是一个例子
结果create_system（RoomSystem ** sys）{
活动*（（* sys） - > c_array）= malloc（num_challenges *的sizeof（活动））; 
} 

解决方案

尝试

 c_array =（活动*）calloc（num_challenges， sizeof （活动））; 

< blockquote>内存分配调用正确但分配错误。通过以类型 Activity * 开始行，您告诉编译器创建一个在类型后指定名称的局部变量。但是该名称无效，因为它包含不允许的字符，您可能不想创建局部变量，而是将已分配的内存分配给传递的结构。



如果你拥有现有 RoomSystem 结构的地址 * sys ：

 sys-> c_array = malloc（num_challenges * sizeof（Activity））; 

如果你的函数有 RoomSystem ** sys 参数：

结果create_system（RoomSystem ** sys）
 {
 * sys-> c_array = malloc（num_challenges *的sizeof（活动））; 
 / *假设RESULT_ *是结果值* / 
 return（* sys-> c_array == NULL）？ RESULT_NO_MEM：RESULT_OK; 
} 

i have a function create_system in this function i want to allocate memory to an array called c_array that it's tipe is a pointer to a struct Activity..
i get that the way i tried to allocate the memory is wrong ! i tried everything and i got after searching all over google to this way to allocate :

Activity* ((*sys)->c_array)=malloc(num_challenges * sizeof(Activity));

but i get the follwing mistake :

expected ')' before '->' token

any help of i am doing wrong here ! thank you in advance

What I have tried:

typedef struct SRoomSystem
{
Activity *c_array;

} RoomSystem;
int num_challenges=6;//this is just an example
Result create_system(RoomSystem **sys){
   Activity* ((*sys)->c_array)=malloc(num_challenges * sizeof(Activity));
}

解决方案

Try

c_array = (Activity *)calloc( num_challenges, sizeof(Activity) );

The memory allocation call is correct but the assignment is wrong. By starting the line with the type Activity* you are telling the compiler to create a local variable with the name specified after the type. But that name is invalid because it contains unallowed characters and you probably don't want to create a local variable but assign the allocated memory to the passed structure.

If you have the address *sys of an existing RoomSystem structure:

sys->c_array = malloc(num_challenges * sizeof(Activity));

If you have a function with a RoomSystem **sys parameter:

Result create_system(RoomSystem **sys)
{
    *sys->c_array = malloc(num_challenges * sizeof(Activity));
    /* Assuming RESULT_* are Result values */
    return (*sys->c_array == NULL) ? RESULT_NO_MEM : RESULT_OK;
}

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