使用mmap在C中構建共享內存

Question

我已經閱讀過早期的問題和對我的問題的解答，但大多數人似乎使用shmget而不是mmap。

我正在使用mmap作爲共享內存，它一切正常，直到我從使用靜態變量改爲結構。目前，我發現了以下錯誤：

server.c: In function ‘interfaceComms’: 
server.c:129:18: error: ‘interfaceConnection’ undeclared (first use in this function) 
    n = write(sock, interfaceConnection->processingResults, 47); 
       ^
server.c:129:18: note: each undeclared identifier is reported only once for each function it appears in 
server.c:139:12: error: ‘imageDetails’ undeclared (first use in this function) 
    if(strcmp(imageDetails->prevImage, "") != 0) { 
      ^
server.c: In function ‘robotComms’: 
server.c:162:2: error: ‘imageDetails’ undeclared (first use in this function) 
    imageDetails->prevImage = imageDetails->currImage; 
^
server.c:213:9: error: ‘interfaceConnection’ undeclared (first use in this function) 
    strcpy(interfaceConnection->processingResults, msg); 

我理解錯誤，但我不知道如何使用它結構，因爲這是我想共享內存做的方式來解決。我是分叉的，所以這些結構正在用於兒童流程。

我的代碼：

typedef struct Images { 
    char prevImage; 
    char currImage; 
} image; 

typedef struct Robot { 
    char coordinates; 
} robot; 

typedef struct Interface { 
    char processingResults; 
} interface; 

int main(int argc, char *argv[]){ 
int sockfd, newsockfd, portno, clilen, memid; 
char buffer[256]; 
struct sockaddr_in serv_addr, cli_addr; 
int n, pid; 
interface *interfaceConnection; 
image *imageDetails; 

// First call to socket() function 
sockfd = socket(AF_INET, SOCK_STREAM, 0); 

if (sockfd < 0){ 
    perror("Error opening socket"); 
    exit(1); 
} 

// Initialise socket structure 
bzero((char *) &serv_addr, sizeof(serv_addr)); 
portno = 5001; 

serv_addr.sin_family = AF_INET; 
serv_addr.sin_addr.s_addr = INADDR_ANY; 
serv_addr.sin_port = htons(portno); 

//Bind the socket 
if(bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr)) < 0){ 
    perror("Error binding socket"); 
    exit(1); 
} 

//Listen for client connections 
listen(sockfd,5); 
clilen = sizeof(cli_addr); 

//Share memory before forking 
interfaceConnection = mmap(NULL, sizeof(interface), PROT_READ | PROT_WRITE, 
       MAP_SHARED | MAP_ANONYMOUS, -1, 0); 

imageDetails = mmap(NULL, sizeof(image), PROT_READ | PROT_WRITE, 
      MAP_SHARED | MAP_ANONYMOUS, -1, 0); 

函數 'interfaceComms' 和 'robotComms' 被稱爲後來叉發生後。但我猜我的問題在那裏。

按照要求，intefaceComms和robotComms功能：

void checkMessage(int sock){ 
int n; 
char message[256]; 
n = read(sock, message, 255); 
int response; 

if(n < 0){ 
    perror("Error reading the socket"); 
    exit(1); 
} 

//see if the message is from the robot or from the interface 
if(strstr(message,"robot") != NULL) { 
    //The robot wants the co-ordinates of the component 
    robotComms(sock); 
} else { 
    //Someone has accessed the main page 
    interfaceComms(sock); 
} 
} 

void interfaceComms(int sock) { 
int n; 

n = write(sock, interfaceConnection->processingResults, 47); 

if (n < 0){ 
    perror("Error writing to the socket"); 
    exit(1); 
} else { 
    printf("Results sent to interface\n"); 
} 
} 

void robotComms(int sock) { 
int n; 
srand (time(NULL)); //reset rand 
//printf("Here is the message: %s\n", message); 
printf("Getting image...\n"); 

//Change currImage to prevImage 
imageDetails->prevImage = imageDetails->currImage; 

在此先感謝。

Answer 1

你的問題是，interfaceConnection是你的主函數中的局部變量。

interface *interfaceConnection; 

我假設你想要在全局範圍內。很難說沒有看到其他代碼。