error: incomplete type for struct sembuf

Question

我正在编写一个程序，在并行编程中使用信号量和信号量缓冲区进行互斥。这是导致错误的代码位以及使用 sembuf 指针的信号和等待函数。

#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdlib.h>
#include <unistd.h>
#include <semaphore.h>
#include <pthread.h>
#define NSEMS 1


// semaphore buffers
static struct sembuf OP = {0,-1,0};
static struct sembuf OV = {0,1,0};
struct sembuf *P =&OP;
struct sembuf *V =&OV;


// Wait() function for semaphore
int POP()
{   
int status;
status = semop(sem_id, P,1);
return status;
}

// Signal() function for semaphore
int VOP()
{   
int status;
status = semop(sem_id, V,1);
return status;

这是我收到的错误：

sem.c:17:15: error: variable ‘OP’ has initializer but incomplete type
static struct sembuf OP = {0,-1,0};
           ^
sem.c:17:15: warning: excess elements in struct initializer [enabled by   default]
sem.c:17:15: warning: (near initialization for ‘OP’) [enabled by default]
sem.c:17:15: warning: excess elements in struct initializer [enabled by default]
sem.c:17:15: warning: (near initialization for ‘OP’) [enabled by default]
sem.c:17:15: warning: excess elements in struct initializer [enabled by default]
sem.c:17:15: warning: (near initialization for ‘OP’) [enabled by default]

我收到 OV 结构的相同错误，但我不明白为什么。非常感谢任何帮助。

Answer 1

在使用类型之前，您需要包含必要的 headers...

你的情况：

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>