我正在尝试编写一个将记录写入共享内存对象的函数，但是我一直在遇到段错误。当我用valgrind调试时，它说“使用大小为8的未初始化值”。这是下面的代码。
这些是我的头文件中的结构（我知道我与驼峰大小写不一致，下划线对不起，对不起。）table_t中的最后两个指针指向共享内存中保存数据块/记录的部分（无效* db）和保存每个记录信息的区域（db_info * dbInfo）。
typedef struct{
int dbInfoId;
int deleted;
}db_info;
typedef struct{
int shm_fd;
int numP;
int control_id;
char *name;
int record_size;
int max_records;
db_info* dbInfo;
void* db;
}table_t;
typedef struct{
int id;
void* record;
}data_block;
这是add_record函数。添加了一些printf语句，所以我知道错误开始之前代码能走多远，并可以打印某些信息。
int add_record(table_t *tbl, void *record, int record_size){
printf("code gets this far\n");
size_t size = sizeof(record_size);
data_block* rec;
db_info* recInfo;
tbl->control_id += 1;
printf("cid %d\n", tbl->control_id);
printf("code reaches this point\n");
/*according to valgrind issuse start here*/
rec->id = tbl->control_id;
printf("rec id %d", rec->id);
rec->record = record;
printf("code reaches this point\n");
memcpy(tbl->db, rec, size);
recInfo->dbInfoId = rec->id;
recInfo->deleted = 1;
tbl->db += sizeof(rec);
tbl->dbInfo += sizeof(recInfo);
return rec->id;
这是我在add函数中使用的主要内容
#include <sys/stat.h>
#include "data_table.h"
#define MAX_RECORDS 2000000
#define RECORD_SIZE 1024
#define SHM_NAME "abe"
int main(){
table_t* tbl;
table_t controlBlock;
db_info info;
int com;
int loop = 0;
int recId;
char* rec = "hello world";
tbl = open_table(SHM_NAME, RECORD_SIZE, MAX_RECORDS);
printf("this is the number of processes %d\n", tbl->numP);
tbl->name = SHM_NAME;
/*this is where i set the pointers to their required locations*/
tbl->dbInfo = tbl + sizeof(controlBlock);
tbl->db = tbl + sizeof(tbl->dbInfo);
/*printing out the different address locations*/
printf("This is the cb %d, This is the dbInfo %d, and this is the db %d\n",
&tbl, &tbl->dbInfo, &tbl->db);
/* my loop. I havent finished all the commands yet*/
while(loop == 0){
printf("enter a command (just the number):\n");
printf("1. Add\n2. Delete\n3. Process\n4. Close\n5. # of processes\n");
printf("6. exit\n");
scanf("%d", &com);
if(com == 1){
recId = add_record(tbl, rec, RECORD_SIZE);
printf("record added ID: %d\n", &recId);
}
else if(com == 4){
close_table(tbl);
loop++;
}
else if(com == 5){
printf("process count %d\n", tbl->numP);
}
else if(com == 6){
loop++;
}
}
最后是来自valgrind的错误
this is the number of processes 4
This is the cb -16777872, This is the dbInfo 90521632, and this is the db 90521640
enter a command (just the number):
1. Add
2. Delete
3. Process
4. Close
5. # of processes
6. exit
1
code gets this far
cid 4
code reaches this point
==4042== Use of uninitialised value of size 8
==4042== at 0x108BDA: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Use of uninitialised value of size 8
==4042== at 0x108BE0: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Use of uninitialised value of size 8
==4042== at 0x108BFD: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
rec id 4code reaches this point
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C366F2: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C36702: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C36707: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C36729: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Use of uninitialised value of size 8
==4042== at 0x4C36750: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Use of uninitialised value of size 8
==4042== at 0x4C36753: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C3675F: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Use of uninitialised value of size 8
==4042== at 0x108C2C: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== Use of uninitialised value of size 8
==4042== at 0x108C32: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== Process terminating with default action of signal 11 (SIGSEGV)
==4042== Bad permissions for mapped region at address 0x1088A0
==4042== at 0x108C32: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
--4042-- REDIR: 0x50db950 (libc.so.6:free) redirected to 0x4c30cd0 (free)
==4042==
==4042== HEAP SUMMARY:
==4042== in use at exit: 0 bytes in 0 blocks
==4042== total heap usage: 2 allocs, 2 frees, 2,048 bytes allocated
==4042==
==4042== All heap blocks were freed -- no leaks are possible
==4042==
==4042== Use --track-origins=yes to see where uninitialised values come from
==4042== ERROR SUMMARY: 14 errors from 12 contexts (suppressed: 0 from 0)
==4042==
==4042== 1 errors in context 1 of 12:
==4042== Use of uninitialised value of size 8
==4042== at 0x108C32: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 2 of 12:
==4042== Use of uninitialised value of size 8
==4042== at 0x108C2C: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 3 of 12:
==4042== Use of uninitialised value of size 8
==4042== at 0x4C36750: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 4 of 12:
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C36729: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 5 of 12:
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C36707: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 6 of 12:
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C36702: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 7 of 12:
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C366F2: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 8 of 12:
==4042== Use of uninitialised value of size 8
==4042== at 0x108BFD: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 9 of 12:
==4042== Use of uninitialised value of size 8
==4042== at 0x108BE0: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 1 errors in context 10 of 12:
==4042== Use of uninitialised value of size 8
==4042== at 0x108BDA: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 2 errors in context 11 of 12:
==4042== Conditional jump or move depends on uninitialised value(s)
==4042== at 0x4C3675F: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042==
==4042== 2 errors in context 12 of 12:
==4042== Use of uninitialised value of size 8
==4042== at 0x4C36753: memmove (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==4042== by 0x108C27: add_record (in /home/abiodun/Documents/Comp 3713/Assignment3_makeup/main)
==4042== by 0x108DAA: main (main.c:35)
==4042==
==4042== ERROR SUMMARY: 14 errors from 12 contexts (suppressed: 0 from 0)
Segmentation fault (core dumped)
[我知道这很多，而且我的概率很多，但我以前从未使用过共享内存，并且已经尝试解决了几个小时。
这是open_table函数。它以前工作过，但现在我遇到了段错误，所以我不确定。
table_t *open_table(char *name, int record_size, int max_records){
int shm_fd;
int table_size;
void* ptr;
table_t* tbl;
table_t controlBlock;
db_info info;
data_block data;
table_size = max_records * sizeof(controlBlock) * sizeof(info) *
sizeof(data);
if((shm_fd = shm_open(name, O_CREAT | O_RDWR, 0666)) == -1){
exit(EXIT_FAILURE);
}
ftruncate(shm_fd, table_size);
ptr = mmap(NULL, table_size, PROT_WRITE | PROT_READ, MAP_SHARED, shm_fd,
0);
tbl = ptr;
tbl->shm_fd = shm_fd;
tbl->max_records = max_records;
tbl->record_size = record_size;
if(tbl->numP >= 1){
tbl->numP += 1;
}
else{
tbl->numP = 1;
}
return tbl;
}
对代码混乱感到抱歉