如何进行这种类型的转换？ [英] How can I do this type conversion?

问题描述

我的代码在这里。

  struct process * init_process（char * programName，int startTime，int cpuTime）{
 struct process * proc; 
 proc =（malloc（sizeof（struct process）））; 
 if（proc == NULL）{
 printf（致命错误：内存分配失败。\\\
Terminating.\\\
）; 
 exit（1）; 
} 
 proc-> programName = programName; 
 proc-> cpuTime = cpuTime; 
 proc-> startTime = startTime; 
 proc-> next = NULL; 
 return（proc）; 
}; 
  

编译器说错误：从'void *'到'process *'的无效转换
我尝试使用进程*（malloc（sizeof（struct process）））做类型转换，但编译器说'错误：期望主表达式之前'*'令牌'这一次。 / p>

任何人都可以帮我解决这个问题吗？

解决方案

您应该使用新样式casts：

  proc = static_cast< process *>（malloc（sizeof（struct process））） ; 
  

但是，如果你真的使用C ++编译器，你应该使用 new / new [] 用于动态分配（和 delete / delete [] 用于重新分配）。

  proc = 
  

如果要将C代码移植到C ++，并且不想修改当前 malloc（）调用，您可以尝试添加：

  #ifdef __cplusplus 
 namespace cxx {
 class voidptr {
 void * p_; 
 public：
 voidptr（void * p = 0）：p_（p）{} 
 template< typename T& 
 operator T *（）const {return static_cast< T *>（p_）; } 
}; 
 voidptr malloc（size_t sz）{return :: malloc（sz）; } 
 voidptr calloc（size_t cnt，size_t sz）{return :: calloc（cnt，sz）; } 
 voidptr realloc（void * p，size_t newsz）{return :: realloc（p，newsz）; } 
} 
 #define malloc（x）cxx :: malloc（x）
 #define calloc（x，y）cxx :: calloc（x，y）
 #define realloc（x，y）cxx :: realloc（x，y）
 #endif 
  

适用于C. 适用于C ++。

My code is here.

struct process *init_process (char *programName, int startTime, int cpuTime) {
    struct process *proc;
    proc = (malloc(sizeof(struct process)));
    if (proc == NULL) {
        printf("Fatal error: memory allocation failure.\nTerminating.\n");
        exit(1);
    }
    proc->programName = programName;
    proc->cpuTime = cpuTime;
    proc->startTime = startTime;
    proc->next = NULL;
    return(proc);
};

The compiler says that "error: invalid conversion from ‘void*’ to ‘process*’" in line 3. I try to use process*(malloc(sizeof(struct process))) to do the type conversion but the compiler says that 'error: expected primary-expression before ‘*’ token' this time.

Can anyone help me solve this problem?

解决方案

In C++, you should use the new style casts:

    proc = static_cast<process *>(malloc(sizeof(struct process)));

But, if you really are using a C++ compiler, you should really be using new/new[] for dynamic allocation (and delete/delete[] for deallocation).

    proc = new process;

If you are porting C code to C++, and you don't want to modify the current malloc() calls, you can try adding this:

#ifdef __cplusplus
namespace cxx {
    class voidptr {
        void *p_;
    public:
        voidptr (void *p = 0) : p_(p) {}
        template <typename T>
        operator T * () const { return static_cast<T *>(p_); }
    };
    voidptr malloc (size_t sz) { return ::malloc(sz); }
    voidptr calloc (size_t cnt, size_t sz) { return ::calloc(cnt, sz); }
    voidptr realloc (void *p, size_t newsz) { return ::realloc(p, newsz); }
}
#define malloc(x) cxx::malloc(x)
#define calloc(x,y) cxx::calloc(x,y)
#define realloc(x,y) cxx::realloc(x,y)
#endif

Works for C. Works for C++.

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