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c++从内存中读取文件内容，内容写到内存 实现文件的内存共享代码实例

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使用c++代码进行内存共享操作，内存共享可以通过key value的形式来保存内存，后面可以使用key值来直接读取内存，效率会很高/

函数说明：

shmget(key_t key, size_t size, int shmflg)(得到一个共享内存标识符或创建一个共享内存对象)

shmflg参数为模式标志参数，使用时需要与IPC对象存取权限（如0600）进行|运算来确定信号量集的存取权限

shmat(int shmid, const void *shmaddr, int shmflg)(把共享内存区对象映射到调用进程的地址空间)

shmdt(const void *shmaddr)(断开共享内存连接)

shmctl(int shmid, int cmd, struct shmid_ds *buf)(共享内存管理)

cmd
IPC_RMID：删除这片共享内存

把内容写到内存代码：

write.cpp文件：

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#include   <string.h>
//#include   <math.h>
//#include   <climits>
//#include   <regex.h>
//#include   <sstream>
#include   <iostream>
#include   <stdio.h>
//#include   <list>
//#include   <vector>
//#include   <time.h>
//#include   <set>
//#include   <algorithm>
//#include   <iterator>
//#include   <sys/time.h>
#include    <sys/ipc.h>
#include    <sys/shm.h>
#include    <sys/types.h>
//#include  <unistd.h>
//#include  <string.h>
//#include   <io.h>
 
 
using namespace std;
 
typedef struct{
    char name[8];
    int age;
} people;
 
#define IPCKEY 0x11
 
#define SHMNAME "shm_ram"
#define OPEN_FLAG O_RDWR|O_CREAT
#define OPEN_MODE 00777
#define FILE_SIZE 4096 * 4
#define LINE_SIZE 1024 * 3
 
 
 
 
int main() {
//  char buff[LINE_SIZE];
//
//  FILE* fp = fopen("sightline.xml", "r");
//  if (NULL == fp) {
//      cout << "open failure" << endl;
//      return 0;
//  }
//
//  while(!feof(fp)){
//      memset(buff, 0, LINE_SIZE);
//      fgets(buff, 1024, fp);
//      cout << buff;
//  }
//
//  fclose(fp);
 
    cout << "Content-type: text/html; charset=\"utf-8\" \n\n";
 
    int shm_id, i;
    key_t key;
    char temp[8];
    people *p_map;
    char pathname[30];
    strcpy(pathname, ".");
    key = ftok(pathname, 0);
    if (key == -1) {
//      perror("ftok error");
        cout << "ftok error" << endl;
        return 0;
    }
 
    cout << "key=" << key << endl;
    //printf("key=%d\n", key);
    shm_id = shmget(key, 1024 * 4, IPC_CREAT | 0666);
    if (shm_id == -1) {
//      perror("shmget error");
        cout << "shmget error" << endl;
        return 0;
    }
 
    //delete
    shmctl(shm_id, IPC_RMID, NULL) ;
 
    shm_id = shmget(key, 1024 * 4, IPC_CREAT | 0666);
    if (shm_id == -1) {
//      perror("shmget error");
        cout << "shmget error" << endl;
        return 0;
    }
 
    cout << "shm_id=" << shm_id << endl;
//  printf("shm_id=%d\n", shm_id);
    p_map = (people*)shmat(shm_id, NULL, 0);
    memset(temp, 0x00, sizeof(temp));
    strcpy(temp, "test");
    temp[4] = '0';
    for (i = 0; i < 7; i++) {
        temp[4] += 1;
        strncpy((p_map + i)->name, temp, 5);
        (p_map + i)->age = 0 + i + 1;
    }
    shmdt(p_map);
 
    cout << "success" << endl;
 
//  int shm_id, i;
//  key_t key;
//  people *p_map;
////    char pathname[30];
////    strcpy(pathname, "/tmp");
//  key = ftok("../test", IPCKEY);
//  if (key == -1) {
////        cout << "ftok error");
//      cout << "ftok error" << endl;
//      return -1;
//  }
////    printf("key=%d\n", key);
//  cout << "key=" << key << endl;
//  shm_id = shmget(key, 0, 0);
//  if (shm_id == -1) {
////        cout << "shmget error");
//      cout << "shmget error" << endl;
//      return -1;
//  }
////    printf("shm_id=%d\n", shm_id);
//  cout << "shm_id=" << shm_id << endl;
//  p_map = (people*) shmat(shm_id, NULL, 0);
//  for (i = 0; i < 3; i++) {
////        printf("name:%s\n", (*(p_map + i)).name);
////        printf("age %d\n", (*(p_map + i)).age);
//      cout << "name=" << (*(p_map + i)).name << endl;
//      cout << "age=" << (*(p_map + i)).age << endl;
//  }
//  if (shmdt(p_map) == -1) {
//      cout << "detach error");
//      return -1;
//  }
 
    return 0;
}

 编译  g++  write.cpp  -o write

执行 ./write

read.cpp

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#include   <string.h>
#include   <math.h>
#include   <climits>
#include   <regex.h>
#include   <sstream>
#include   <iostream>
#include   <stdio.h>
#include   <list>
#include   <vector>
#include   <time.h>
#include   <set>
#include   <algorithm>
#include   <iterator>
#include   <sys/time.h>
#include    <fstream>
#include    <iomanip>
//#include  <stdio.h>
#include    <sys/ipc.h>
#include    <sys/shm.h>
#include    <sys/types.h>
#include    <unistd.h>
//#include  <string.h>
//#include   <io.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
 
 
using namespace std;
 
typedef struct{
    char name[8];
    int age;
} people;
 
#define IPCKEY 0x11
 
#define SHMNAME "shm_ram"
#define OPEN_FLAG O_RDWR|O_CREAT
#define OPEN_MODE 00777
#define FILE_SIZE 4096 * 4
#define LINE_SIZE 1024 * 3
 
 
 
int main() {
//  char buff[LINE_SIZE];
//
//  FILE* fp = fopen("sightline.xml", "r");
//  if (NULL == fp) {
//      cout << "open failure" << endl;
//      return 0;
//  }
//
//  while(!feof(fp)){
//      memset(buff, 0, LINE_SIZE);
//      fgets(buff, 1024, fp);
//      cout << buff;
//  }
//
//  fclose(fp);
 
    cout << "Content-type: text/html; charset=\"utf-8\" \n\n";
 
    int shm_id, i;
    key_t key;
    people *p_map;
    char pathname[30];
    strcpy(pathname, ".");
    key = ftok(pathname, 0);
    if (key == -1) {
        cout << "ftok error" << endl;
        return 0;
    }
 
    cout << "key=" << key << endl;
    shm_id = shmget(key, 0, 0);
    if (shm_id == -1) {
        cout << "shmget error" << endl;
        return -1;
    }
    cout << "shm_id=" << shm_id << endl;
 
    p_map = (people*) shmat(shm_id, NULL, 0);
    for (i = 0; i < 3; i++) {
        cout << "name=" << (*(p_map + i)).name << endl;
        cout << "age=" << (*(p_map + i)).age << endl;
    }
 
    if (shmdt(p_map) == -1) {
        cout << "detach error" << endl;
        return -1;
    }
 
    return 0;
}

 编译  g++  read.cpp  -o read

执行 ./read

来源：//作者：/更新时间：2014-03-18
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