1. 编辑程序

vim shmtool.c

#include <stdio.h> 
#include <sys/types.h> 
#include <sys/ipc.h> 
#include <sys/shm.h> 
#define SEGSIZE 100 
main(int argc, char *argv[]) 
{ key_t key; 
 int shmid, cntr; 
 char *segptr; 
 if(argc == 1) 
 usage(); /* Create unique key via call to ftok() */ 
 key = ftok(".", 'S'); 
 /* Open the shared memory segment - create if necessary */ 
 if((shmid = shmget(key, SEGSIZE, IPC_CREAT|IPC_EXCL|0666)) == -1) 
 { 
 printf("Shared memory segment exists - opening as client\n"); 
 /* Segment probably already exists - try as a client */ 
 if((shmid = shmget(key, SEGSIZE, 0)) == -1) 
 { 
 perror("shmget"); 
 exit(1); 
 } 
 } 
 else 
 { 
 printf("Creating new shared memory segment\n"); 
 } 
 /* Attach (map) the shared memory segment into the current process */ 
 if((segptr = shmat(shmid, 0, 0)) == -1) 
 { 
 perror("shmat"); 
 exit(1); 
 } 
 switch(tolower(argv[1][0])) 
 { 
 case 'w': writeshm(shmid, segptr, argv[2]); 
 break; 
 case 'r': readshm(shmid, segptr); 
 break; 
 case 'd': removeshm(shmid); 
 break; 
 case 'm': changemode(shmid, argv[2]); 
 break; 
 default: usage(); 
 } 
} 
writeshm(int shmid, char *segptr, char *text) 
{ 
 strcpy(segptr, text); 
 printf("Done...\n"); 
} 
readshm(int shmid, char *segptr) 
{ 
 printf("segptr: %s\n", segptr); 
} 
removeshm(int shmid) 
{ 
 shmctl(shmid, IPC_RMID, 0); 
 printf("Shared memory segment marked for deletion\n"); 
} 
changemode(int shmid, char *mode) 
{ 
 struct shmid_ds myshmds; 
 /* Get current values for internal data structure */ 
 shmctl(shmid, IPC_STAT, &myshmds); /* Display old permissions */ 
 printf("Old permissions were: %o\n", myshmds.shm_perm.mode); 
 /* Convert and load the mode */ 
 sscanf(mode, "%o", &myshmds.shm_perm.mode); /* Update the mode */ 
 shmctl(shmid, IPC_SET, &myshmds); 
 printf("New permissions are : %o\n", myshmds.shm_perm.mode); 
} 
usage() 
{ 
 fprintf(stderr, "shmtool - A utility for tinkering with shared memory\n"); 
 fprintf(stderr, "\nUSAGE: shmtool (w)rite <text>\n"); 
 fprintf(stderr, " (r)ead\n"); 
 fprintf(stderr, " (d)elete\n"); 
 fprintf(stderr, " (m)ode change <octal mode>\n"); 
 exit(1); 
}

3. 编译程序

编译文件 shmtool.c 为可执行文件 shmtool

gcc shmtool.c -o shmtool

4. 执行程序

./shmtool

./shmtool w helloworld!

./shmtool r