请问怎么用mmap来存储两个结构体数据

我要思考

mmap.c

#include <stdio.h> #include <fcntl.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <assert.h> #include <sys/stat.h> #include <sys/mman.h> #include <sys/types.h> struct record { &nbsp;&nbsp;&nbsp;&nbsp;unsigned int hash; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int key; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int value; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int offest; }; struct xmap { &nbsp;&nbsp;&nbsp;&nbsp;struct record *records; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int records_count; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int size_index; }; struct xmap *alloc_user_def_t(int fd) { &nbsp;&nbsp;&nbsp;&nbsp;struct xmap   *p; &nbsp;&nbsp;&nbsp;&nbsp;struct record *recs; &nbsp;&nbsp;&nbsp;&nbsp;p = (struct xmap *)mmap(NULL, sizeof(struct xmap) + sizeof(struct record) * 20, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); &nbsp;&nbsp;&nbsp;&nbsp;if (p == NULL) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return NULL; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;p->records = calloc(20, sizeof(struct record)); &nbsp;&nbsp;&nbsp;&nbsp;recs       = p->records; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;recs[0].hash   = 9832; &nbsp;&nbsp;&nbsp;&nbsp;recs[0].key    = 87643; &nbsp;&nbsp;&nbsp;&nbsp;recs[0].value  = 980; &nbsp;&nbsp;&nbsp;&nbsp;recs[0].offest = 987; &nbsp;&nbsp;&nbsp;&nbsp;recs[1].hash   = 8982; &nbsp;&nbsp;&nbsp;&nbsp;recs[1].key    = 907; &nbsp;&nbsp;&nbsp;&nbsp;recs[1].value  = 243; &nbsp;&nbsp;&nbsp;&nbsp;recs[1].offest = 124; &nbsp;&nbsp;&nbsp;&nbsp;p->size_index    = 9897; &nbsp;&nbsp;&nbsp;&nbsp;p->records_count = 67; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;return p; } int main() { &nbsp;&nbsp;&nbsp;&nbsp;int fd, i; &nbsp;&nbsp;&nbsp;&nbsp;struct xmap *ptr; &nbsp;&nbsp;&nbsp;&nbsp;struct record *recs; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;fd    = open("data.mmap", O_CREAT|O_RDWR, 0777); &nbsp;&nbsp;&nbsp;&nbsp;lseek(fd, (sizeof(struct xmap) + sizeof(struct record) * 20) -1 , SEEK_SET); &nbsp;&nbsp;&nbsp;&nbsp;write(fd,"",1); &nbsp;&nbsp;&nbsp;&nbsp;ptr  = alloc_user_def_t(fd); &nbsp;&nbsp;&nbsp;&nbsp;recs = ptr->records; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[0].hash = %d\r\n", recs[0].hash); &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[0].key  = %d\r\n", recs[0].key); &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[1].hash = %d\r\n", recs[1].hash); &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[1].key  = %d\r\n", recs[1].key); &nbsp;&nbsp;&nbsp;&nbsp;printf("ptr->size_index = %d\r\n", ptr->size_index); &nbsp;&nbsp;&nbsp;&nbsp;munmap(ptr, sizeof(struct xmap) + sizeof(struct record) * 20); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;free(recs); &nbsp;&nbsp;&nbsp;&nbsp;close(fd); &nbsp;&nbsp;&nbsp;&nbsp;return 0; }

mmap_read.c

#include <stdio.h> #include <fcntl.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <assert.h> #include <sys/stat.h> #include <sys/mman.h> #include <sys/types.h> struct record { &nbsp;&nbsp;&nbsp;&nbsp;unsigned int hash; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int key; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int value; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int offest; }; struct xmap { &nbsp;&nbsp;&nbsp;&nbsp;struct record *records; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int records_count; &nbsp;&nbsp;&nbsp;&nbsp;unsigned int size_index; }; int main() { &nbsp;&nbsp;&nbsp;&nbsp;int fd, i; &nbsp;&nbsp;&nbsp;&nbsp;struct xmap *ptr; &nbsp;&nbsp;&nbsp;&nbsp;struct record *recs; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;fd    = open("data.mmap", O_CREAT|O_RDWR, 0777); &nbsp;&nbsp;&nbsp;&nbsp;ptr  = (struct xmap *)mmap(NULL, sizeof(struct xmap) + sizeof(struct record) * 20, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); &nbsp;&nbsp;&nbsp;&nbsp;recs = ptr->records; &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[0].hash = %d\r\n", recs[0].hash); &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[0].key  = %d\r\n", recs[0].key); &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[1].hash = %d\r\n", recs[1].hash); &nbsp;&nbsp;&nbsp;&nbsp;printf("recs[1].key  = %d\r\n", recs[1].key); &nbsp;&nbsp;&nbsp;&nbsp;printf("ptr->size_index = %d\r\n", ptr->size_index); &nbsp;&nbsp;&nbsp;&nbsp;munmap(ptr, sizeof(struct xmap) + sizeof(struct record) * 20); &nbsp;&nbsp;&nbsp;&nbsp; &nbsp;&nbsp;&nbsp;&nbsp;close(fd); &nbsp;&nbsp;&nbsp;&nbsp;return 0; }

mmap_read.c

        recs = ptr->records;
       
        printf("recs[0].hash = %d\r\n", recs[0].hash);
        printf("recs[0].key  = %d\r\n", recs[0].key);
        printf("recs[1].hash = %d\r\n", recs[1].hash);
        printf("recs[1].key  = %d\r\n", recs[1].key);

执行到这里 就有错误


struct xmap 结构体的 struct record *records; 大小是动态的

请大家帮我看看 怎么做用mmap 来保存这些数据

iunknown

在 mmap.c 里面需要修改两个地方：

1. p->records = calloc(20, sizeof(struct record));

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修改为

1. p->records = (struct record*)(((char*)p) + sizeof( xmap) );

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calloc 分配的内存不是在 mmap 出来的范围内的。看代码的原意，应该是上面修改后的意思吧。
修改之后的代码也不能保证总是正确。根本解决方法是在 xmap 里面不要用指针，因为指针式不能跨进程。
所有要用到指针的地方，改为用相对于开始位置（p）的 offset 来表示。

删除

1. free(recs);

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运行结果为：

1. 
   
2. bash$ ./w
   
3. recs[0].hash = 9832
   
4. recs[0].key  = 87643
   
5. recs[1].hash = 8982
   
6. recs[1].key  = 907
   
7. ptr->size_index = 9897
   
8. 
   
9. bash$ ./r
   
10. recs[0].hash = 9832
    
11. recs[0].key  = 87643
    
12. recs[1].hash = 8982
    
13. recs[1].key  = 907
    
14. ptr->size_index = 9897
    

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[ 本帖最后由 iunknown 于 2008-2-20 13:18 编辑 ]