如何在Linux中使用C共享内存
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我的一个项目有一个问题。
我一直试图找到一个很好的文档示例，将共享内存与ѭ0一起使用，但没有成功。
基本上情况是，当用户启动程序时，我需要在共享内存中存储两个值：current_path，它是一个char *； file_name，它也是char *。
根据命令参数，以“ 0”开始一个新进程，该进程需要读取和修改共享内存中存储的current_path变量，而file_name变量为只读。
是否有关于共享内存的很好的教程，并带有示例代码（如果可能），您可以将其引导至？
谢谢，
bleepzter
没有找到相关结果
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5 个回复
渴翅吮斡撤
和。我将讨论，因为它更现代，更灵活，但是如果您想使用老式工具，可以看看（或本教程）。 “ 6”功能可用于分配具有高度可自定义参数的内存缓冲区，以控制访问和权限，并在必要时通过文件系统存储支持它们。 以下函数创建一个内存缓冲，进程可以与其子进程共享该缓冲区：#include <stdio.h> #include <stdlib.h> #include <sys/mman.h> void* create_shared_memory(size_t size) { // Our memory buffer will be readable and writable: int protection = PROT_READ | PROT_WRITE; // The buffer will be shared (meaning other processes can access it), but // anonymous (meaning third-party processes cannot obtain an address for it), // so only this process and its children will be able to use it: int visibility = MAP_SHARED | MAP_ANONYMOUS; // The remaining parameters to `mmap()` are not important for this use case, // but the manpage for `mmap` explains their purpose. return mmap(NULL, size, protection, visibility, -1, 0); }#include <string.h> #include <unistd.h> int main() { char* parent_message = \"hello\"; // parent process will write this message char* child_message = \"goodbye\"; // child process will then write this one void* shmem = create_shared_memory(128); memcpy(shmem, parent_message, sizeof(parent_message)); int pid = fork(); if (pid == 0) { printf(\"Child read: %s\\n\", shmem); memcpy(shmem, child_message, sizeof(child_message)); printf(\"Child wrote: %s\\n\", shmem); } else { printf(\"Parent read: %s\\n\", shmem); sleep(1); printf(\"After 1s, parent read: %s\\n\", shmem); } }细屠截殴些
#include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> #define SHM_SIZE 1024 /* make it a 1K shared memory segment */ int main(int argc, char *argv[]) { key_t key; int shmid; char *data; int mode; if (argc > 2) { fprintf(stderr, \"usage: shmdemo [data_to_write]\\n\"); exit(1); } /* make the key: */ if ((key = ftok(\"hello.txt\", \'R\')) == -1) /*Here the file must exist */ { perror(\"ftok\"); exit(1); } /* create the segment: */ if ((shmid = shmget(key, SHM_SIZE, 0644 | IPC_CREAT)) == -1) { perror(\"shmget\"); exit(1); } /* attach to the segment to get a pointer to it: */ data = shmat(shmid, NULL, 0); if (data == (char *)(-1)) { perror(\"shmat\"); exit(1); } /* read or modify the segment, based on the command line: */ if (argc == 2) { printf(\"writing to segment: \\\"%s\\\"\\n\", argv[1]); strncpy(data, argv[1], SHM_SIZE); } else printf(\"segment contains: \\\"%s\\\"\\n\", data); /* detach from the segment: */ if (shmdt(data) == -1) { perror(\"shmdt\"); exit(1); } return 0; }筷啸够对铅
#include<sys/ipc.h> #include<sys/shm.h> int shmid; int shmkey = 12222;//u can choose it as your choice int main() { //now your main starting shmid = shmget(shmkey,1024,IPC_CREAT); // 1024 = your preferred size for share memory // IPC_CREAT its a flag to create shared memory //now attach a memory to this share memory char *shmpointer = shmat(shmid,NULL); //do your work with the shared memory //read -write will be done with the *shmppointer //after your work is done deattach the pointer shmdt(&shmpointer, NULL);瓜唱鬼
#include <stdio.h> #include <sys/shm.h> #include <sys/stat.h> int main () { int segment_id; char* shared_memory; struct shmid_ds shmbuffer; int segment_size; const int shared_segment_size = 0x6400; /* Allocate a shared memory segment. */ segment_id = shmget (IPC_PRIVATE, shared_segment_size, IPC_CREAT | IPC_EXCL | S_IRUSR | S_IWUSR); /* Attach the shared memory segment. */ shared_memory = (char*) shmat (segment_id, 0, 0); printf (\"shared memory attached at address %p\\n\", shared_memory); /* Determine the segment\'s size. */ shmctl (segment_id, IPC_STAT, &shmbuffer); segment_size = shmbuffer.shm_segsz; printf (\"segment size: %d\\n\", segment_size); /* Write a string to the shared memory segment. */ sprintf (shared_memory, \"Hello, world.\"); /* Detach the shared memory segment. */ shmdt (shared_memory); /* Reattach the shared memory segment, at a different address. */ shared_memory = (char*) shmat (segment_id, (void*) 0x5000000, 0); printf (\"shared memory reattached at address %p\\n\", shared_memory); /* Print out the string from shared memory. */ printf (\"%s\\n\", shared_memory); /* Detach the shared memory segment. */ shmdt (shared_memory); /* Deallocate the shared memory segment. */ shmctl (segment_id, IPC_RMID, 0); return 0; }栖很钾是狠
#include <sys/mman.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> /* * pvtmMmapAlloc - creates a memory mapped file area. * The return value is a page-aligned memory value, or NULL if there is a failure. * Here\'s the list of arguments: * @mmapFileName - the name of the memory mapped file * @size - the size of the memory mapped file (should be a multiple of the system page for best performance) * @create - determines whether or not the area should be created. */ void* pvtmMmapAlloc (char * mmapFileName, size_t size, char create) { void * retv = NULL; if (create) { mode_t origMask = umask(0); int mmapFd = open(mmapFileName, O_CREAT|O_RDWR, 00666); umask(origMask); if (mmapFd < 0) { perror(\"open mmapFd failed\"); return NULL; } if ((ftruncate(mmapFd, size) == 0)) { int result = lseek(mmapFd, size - 1, SEEK_SET); if (result == -1) { perror(\"lseek mmapFd failed\"); close(mmapFd); return NULL; } /* Something needs to be written at the end of the file to * have the file actually have the new size. * Just writing an empty string at the current file position will do. * Note: * - The current position in the file is at the end of the stretched * file due to the call to lseek(). * - The current position in the file is at the end of the stretched * file due to the call to lseek(). * - An empty string is actually a single \'\\0\' character, so a zero-byte * will be written at the last byte of the file. */ result = write(mmapFd, \"\", 1); if (result != 1) { perror(\"write mmapFd failed\"); close(mmapFd); return NULL; } retv = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, mmapFd, 0); if (retv == MAP_FAILED || retv == NULL) { perror(\"mmap\"); close(mmapFd); return NULL; } } } else { int mmapFd = open(mmapFileName, O_RDWR, 00666); if (mmapFd < 0) { return NULL; } int result = lseek(mmapFd, 0, SEEK_END); if (result == -1) { perror(\"lseek mmapFd failed\"); close(mmapFd); return NULL; } if (result == 0) { perror(\"The file has 0 bytes\"); close(mmapFd); return NULL; } retv = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, mmapFd, 0); if (retv == MAP_FAILED || retv == NULL) { perror(\"mmap\"); close(mmapFd); return NULL; } close(mmapFd); } return retv; }