问题描述
我正在尝试使用 OCI 库在Oracle表中选择一个LONG RAW列。
出于超出此问题范围的原因，我更喜欢分段读取数据，因此不使用回调。
语句的执行按预期返回OCI_NEED_DATA，但是第一次调用OCIStmtFetch会导致系统错误。
错误代码5：在oracommon12.dll中读取地址0的访问冲突。
我有客户端12.1并连接到Oracle 10.g
下面是一个最小化程序，该程序会重现该错误。
一切顺利，直到第43行（结果10）：它输出99等于'OCI_NEED_DATA'。
程序随后使该行崩溃。
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <oci.h>
static const char uid[] = "XXXX";
static const char pswd[] = "XXXX";
static const char conn[] = "XXXX";
static const char fileid[] = "XXXX";
int main(int argc,char argv[])
{
OCIEnv* p_env;
OCIError* p_err;
OCISvcCtx* p_svc;
OCIStmt* p_sql;
OCIDefine* p_dfn;
OCIBind* p_bnd;
int rc;
char stmt[256];
ub1 buffer[8192];
rc = OCIInitialize(OCI_DEFAULT,NULL,(dvoid* (*)(dvoid*,size_t))NULL,dvoid*,(void (*)(dvoid*,dvoid*))NULL);
printf("RESULT 1: %d\n",rc);
rc = OCIEnvInit(&p_env,OCI_DEFAULT,NULL);
printf("RESULT 2: %d\n",rc);
rc = OCIHandleAlloc(p_env,(void**)&p_err,OCI_HTYPE_ERROR,NULL);
printf("RESULT 3: %d\n",(void**)&p_svc,OCI_HTYPE_SVCCTX,NULL);
printf("RESULT 4: %d\n",rc);
rc = OCIlogon(p_env,p_err,&p_svc,(text*)uid,(ub4)strlen(uid),(text*)pswd,(ub4)strlen(pswd),(text*)conn,(ub4)strlen(conn));
printf("RESULT 5: %d\n",(void**)&p_sql,OCI_HTYPE_STMT,NULL);
printf("RESULT 6: %d\n",rc);
sprintf(stmt,"SELECT content FROM td_planimetrie WHERE id_file = :x");
rc = OCIStmtPrepare(p_sql,(text*)stmt,(ub4)strlen(stmt),OCI_NTV_Syntax,OCI_DEFAULT);
printf("RESULT 7: %d\n",rc);
rc = OCIBindByName(p_sql,&p_bnd,(text*)":x",-1,(text*)fileid,(sb4)strlen(fileid) + 1,sqlT_STR,OCI_DEFAULT);
printf("RESULT 8: %d\n",rc);
rc = OCIDefineByPos(p_sql,&p_dfn,1,sqlT_LBI,OCI_DYNAMIC_FETCH);
printf("RESULT 9: %d\n",rc);
rc = OCIStmtExecute(p_svc,p_sql,OCI_DEFAULT);
printf("RESULT 10: %d\n",rc); // <-- rc equals 99=OCI_NEED_DATA
rc = OCIStmtFetch(p_sql,OCI_DEFAULT); // <-- This crashes
printf("RESULT 11: %d\n",rc);
while (rc == OCI_NEED_DATA)
{
void* hndlp;
ub4 type;
ub1 in_out;
ub4 iter;
ub4 idx;
ub1 piece;
ub4 alen;
printf("RESULT 12a\n");
rc = OCIStmtGetPieceInfo(p_sql,&hndlp,&type,&in_out,&iter,&idx,&piece);
printf("RESULT 12b %d,%d,%d\n",(int)rc,(int)type,(int)in_out,(int)iter,(int)idx,(int)piece);
alen = sizeof(buffer);
rc = OCIStmtSetPieceInfo(hndlp,type,buffer,&alen,piece,NULL);
printf("RESULT 12c %d,(int)alen);
rc = OCIStmtFetch(p_sql,OCI_FETCH_NEXT,OCI_DEFAULT);
printf("RESULT 12d: %d\n",rc);
}
printf("RESULT 13: %d\n",rc);
rc = OCIlogoff(p_svc,p_err);
rc = OCIHandleFree(p_sql,OCI_HTYPE_STMT);
rc = OCIHandleFree(p_svc,OCI_HTYPE_SVCCTX);
rc = OCIHandleFree(p_err,OCI_HTYPE_ERROR);
return (0);
} // main
解决方法
我自己弄清楚了：
首先，必须将对OCIStmtExecute的调用中的参数 iters 设置为0。
这样可以避免崩溃，但不能解决整个问题。
此外，对OCIDefineByPos的调用中的参数 value_sz 必须设置为要读取的列的实际大小。
最后，只有在连续调用OCIStmtSetPieceInfo之后，才能读取作为OCIStmtFetch的第4个参数传递的缓冲区。
这将导致以下代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <oci.h>
static const char uid[] = "XXXX";
static const char pswd[] = "XXXX";
static const char conn[] = "XXXX";
static const char fileid[] = "XXXX";
int main(int argc,char argv[])
{
OCIEnv* p_env;
OCIError* p_err;
OCISvcCtx* p_svc;
OCIStmt* p_sql;
OCIDefine* p_dfn;
OCIBind* p_bnd;
int rc;
char stmt[256];
unsigned char buffer[8192];
int counter;
long filesize;
// Connect to DB
rc = OCIInitialize(OCI_DEFAULT,NULL,(dvoid* (*)(dvoid*,size_t))NULL,dvoid*,(void (*)(dvoid*,dvoid*))NULL);
printf("RESULT 1: %d\n",rc);
rc = OCIEnvInit(&p_env,OCI_DEFAULT,NULL);
printf("RESULT 2: %d\n",rc);
rc = OCIHandleAlloc(p_env,(void**)&p_err,OCI_HTYPE_ERROR,NULL);
printf("RESULT 3: %d\n",(void**)&p_svc,OCI_HTYPE_SVCCTX,NULL);
printf("RESULT 4: %d\n",rc);
rc = OCILogon(p_env,p_err,&p_svc,(text*)uid,(ub4)strlen(uid),(text*)pswd,(ub4)strlen(pswd),(text*)conn,(ub4)strlen(conn));
printf("RESULT 5: %d\n",rc);
// Determine size of data
rc = OCIHandleAlloc(p_env,(void**)&p_sql,OCI_HTYPE_STMT,NULL);
printf("RESULT 6: %d\n",rc);
sprintf(stmt,"SELECT filesize FROM td_planimetrie WHERE id_file = :x");
rc = OCIStmtPrepare(p_sql,(text*)stmt,(ub4)strlen(stmt),OCI_NTV_SYNTAX,OCI_DEFAULT);
printf("RESULT 6a: %d\n",rc);
rc = OCIBindByName(p_sql,&p_bnd,(text*)":x",-1,(text*)fileid,(sb4)strlen(fileid) + 1,SQLT_STR,OCI_DEFAULT);
printf("RESULT 6b: %d\n",rc);
rc = OCIDefineByPos(p_sql,&p_dfn,1,&filesize,sizeof(filesize),SQLT_INT,OCI_DEFAULT);
printf("RESULT 6c: %d\n",rc);
rc = OCIStmtExecute(p_svc,p_sql,OCI_DEFAULT);
printf("RESULT 6d: %d %ld\n",rc,filesize);
rc = OCIHandleFree(p_sql,OCI_HTYPE_STMT);
printf("RESULT 6d: %d\n",rc);
// Prepare reading data
rc = OCIHandleAlloc(p_env,NULL);
printf("RESULT 7: %d\n","SELECT content FROM td_planimetrie WHERE id_file = :x");
rc = OCIStmtPrepare(p_sql,OCI_DEFAULT);
printf("RESULT 7a: %d\n",OCI_DEFAULT);
printf("RESULT 8: %d\n",filesize,SQLT_LBI,OCI_DYNAMIC_FETCH);
printf("RESULT 9: %d\n",OCI_DEFAULT);
printf("RESULT 10: %d\n",rc);
rc = OCIStmtFetch(p_sql,OCI_DEFAULT);
printf("RESULT 11: %d\n",rc);
// Read data
unsigned long size_left = filesize;
while (rc == OCI_NEED_DATA)
{
void* hndlp;
ub4 type;
ub1 in_out;
ub4 iter;
ub4 idx;
ub1 piece;
ub4 alen;
rc = OCIStmtGetPieceInfo(p_sql,&hndlp,&type,&in_out,&iter,&idx,&piece);
printf("RESULT 12a %d,%d,%d\n",(int)rc,(int)type,(int)in_out,(int)iter,(int)idx,(int)piece);
alen = sizeof(buffer);
memset(buffer,0xDA,sizeof(buffer)); // some arbitrary data .....
rc = OCIStmtSetPieceInfo(hndlp,type,buffer,&alen,piece,NULL);
printf("RESULT 12b %d,(int)alen);
rc = OCIStmtFetch(p_sql,OCI_DEFAULT);
printf("RESULT 12c: %d\n",rc);
// We can use the buffer over here
long nr_read = (size_left < alen) ? size_left : alen;
// save 'nr_read' bytes within the buffer
size_left -= nr_read;
}
printf("Size left: %lu\n",size_left);
// Cleaning up...
rc = OCILogoff(p_svc,p_err);
rc = OCIHandleFree(p_sql,OCI_HTYPE_STMT);
rc = OCIHandleFree(p_svc,OCI_HTYPE_SVCCTX);
rc = OCIHandleFree(p_err,OCI_HTYPE_ERROR);
return (0);
} // main