我正在尝试使用postgresql在名为xxx的表中更新/更改两列 - comment和id。虽然编译器没有显示任何错误，但Valgrind给出了重大错误。代码是：
int main()
{
PGconn *conn;
PGresult *res;
int i=0,nFields=0,row=0,col=0;
conn = PQconnectdb("dbname=test1 host=localhost user=postgres password=yyy");
if(PQstatus(conn) == CONNECTION_BAD)
{
fprintf(stderr, "Connection to database \"%s\" failed.\n", PQerrorMessage(conn));
fprintf(stderr, "%s", PQerrorMessage(conn));
exit_nicely(conn);
}
res = PQexec(conn, "IF COL_LENGTH('xxx','comment') IS NULL");
if(res)
res = PQexec(conn, "ALTER TABLE xxx ADD comment VARCHAR(500)");
else
res = PQexec(conn, "UPDATE TABLE xxx ADD comment VARCHAR(500)");
res = PQexec(conn, "IF COL_LENGTH('xxx','id') IS NULL");
if(res)
res = PQexec(conn, "ALTER TABLE xxx ADD id VARCHAR(50)");
else
res = PQexec(conn, "UPDATE TABLE xxx ADD id VARCHAR(50)");
res = PQexec(conn, "SELECT * FROM xxx");
if((!res) || (PQresultStatus(res) != PGRES_TUPLES_OK))
{
fprintf(stderr, "SELECT command did not return tuples properly\n");
PQclear(res);
}
PQclear(res);
PQfinish(conn);
return 0;
}
Valgrind发出以下错误：
$ valgrind --track-originins = yes --leak-check = full ./output xaa
==4525== Memcheck, a memory error detector
==4525== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==4525== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==4525== Command: ./Gwidd_uniprot_map2 xaa
==4525==
--4525-- ./Gwidd_uniprot_map2:
--4525-- dSYM directory has wrong UUID; consider using --dsymutil=yes
==4525==
==4525== HEAP SUMMARY:
==4525== in use at exit: 262,994 bytes in 751 blocks
==4525== total heap usage: 1,012 allocs, 261 frees, 345,158 bytes allocated
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are definitely lost in loss record 400 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x10000199A: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are definitely lost in loss record 401 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x1000019B5: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are definitely lost in loss record 402 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x1000019DF: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are definitely lost in loss record 403 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x1000019FA: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== LEAK SUMMARY:
==4525== definitely lost: 800 bytes in 4 blocks
==4525== indirectly lost: 8,192 bytes in 4 blocks
==4525== possibly lost: 0 bytes in 0 blocks
==4525== still reachable: 254,002 bytes in 743 blocks
==4525== suppressed: 0 bytes in 0 blocks
==4525== Reachable blocks (those to which a pointer was found) are not shown.
==4525== To see them, rerun with: --leak-check=full --show-reachable=yes
==4525==
==4525== For counts of detected and suppressed errors, rerun with: -v
==4525== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 0)
请提供解决问题的建议。
修改上述代码：
int main()
{
PGconn *conn;
PGresult *res;
int i=0,nFields=0,row=0,col=0;
conn = PQconnectdb("dbname=test1 host=localhost user=postgres password=madhurima");
if(PQstatus(conn) == CONNECTION_BAD)
{
fprintf(stderr, "Connection to database \"%s\" failed.\n", PQerrorMessage(conn));
fprintf(stderr, "%s", PQerrorMessage(conn));
exit_nicely(conn);
}
res = PQexec(conn, "IF COL_LENGTH('protein_sequence','comment') IS NULL");
PQclear(res);
if(res)
{
res = PQexec(conn, "ALTER TABLE protein_sequence ADD comment VARCHAR(500)");
PQclear(res);
}
else
{
res = PQexec(conn, "UPDATE TABLE protein_sequence ADD comment VARCHAR(500)");
PQclear(res);
}
res = PQexec(conn, "IF COL_LENGTH('protein_sequence','uniprotid') IS NULL");
PQclear(res);
if(res)
{
res = PQexec(conn, "ALTER TABLE protein_sequence ADD uniprotid VARCHAR(50)");
PQclear(res);
}
else
{
res = PQexec(conn, "UPDATE TABLE protein_sequence ADD uniprotid VARCHAR(50)");
PQclear(res);
}
res = PQexec(conn, "SELECT * FROM protein_sequence");
PQclear(res);
if((!res) || (PQresultStatus(res) != PGRES_TUPLES_OK))
{
fprintf(stderr, "SELECT command did not return tuples properly\n");
PQclear(res);
}
PQclear(res);
PQfinish(conn);
return 0;
}
Valgrind的新错误：
==9234== Memcheck, a memory error detector
==9234== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==9234== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==9234== Command: ./Gwidd_uniprot_map2 xaa
==9234==
--9234-- ./Gwidd_uniprot_map2:
--9234-- dSYM directory has wrong UUID; consider using --dsymutil=yes
==9234== Invalid read of size 4
==9234== at 0x1000804CF: PQresultStatus (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A3B: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dff78 is 40 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid read of size 4
==9234== at 0x10007CCCD: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dffe8 is 152 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid read of size 8
==9234== at 0x10007CCE2: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dffe0 is 144 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid read of size 8
==9234== at 0x10007CD26: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013e0008 is 184 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid read of size 8
==9234== at 0x10007CD3F: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dff60 is 16 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid write of size 8
==9234== at 0x10007CD5D: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dff58 is 8 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid write of size 8
==9234== at 0x10007CD69: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dff60 is 16 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid write of size 8
==9234== at 0x10007CD75: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dff70 is 32 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid write of size 8
==9234== at 0x10007CD81: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dfff8 is 168 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid write of size 8
==9234== at 0x10007CD90: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dffe0 is 144 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid write of size 4
==9234== at 0x10007CD9F: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dffe8 is 152 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234== Invalid free() / delete / delete[]
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A72: main (in ./Gwidd_uniprot_map2)
==9234== Address 0x1013dff50 is 0 bytes inside a block of size 200 free'd
==9234== at 0x100010E9F: free (vg_replace_malloc.c:366)
==9234== by 0x10007CDB4: PQclear (in /usr/lib/libpq.5.dylib)
==9234== by 0x100001A2B: main (in ./Gwidd_uniprot_map2)
==9234==
==9234==
==9234== HEAP SUMMARY:
==9234== in use at exit: 254,002 bytes in 743 blocks
==9234== total heap usage: 1,012 allocs, 270 frees, 345,158 bytes allocated
==9234==
==9234== LEAK SUMMARY:
==9234== definitely lost: 0 bytes in 0 blocks
==9234== indirectly lost: 0 bytes in 0 blocks
==9234== possibly lost: 0 bytes in 0 blocks
==9234== still reachable: 254,002 bytes in 743 blocks
==9234== suppressed: 0 bytes in 0 blocks
==9234== Reachable blocks (those to which a pointer was found) are not shown.
==9234== To see them, rerun with: --leak-check=full --show-reachable=yes
==9234==
==9234== For counts of detected and suppressed errors, rerun with: -v
==9234== ERROR SUMMARY: 12 errors from 12 contexts (suppressed: 0 from 0)
答案 0 :(得分：1)
请考虑代码中的以下代码段：
res = PQexec(conn, "IF COL_LENGTH('xxx','comment') IS NULL");
if(res)
res = PQexec(conn, "ALTER TABLE xxx ADD comment VARCHAR(500)");
else
res = PQexec(conn, "UPDATE TABLE xxx ADD comment VARCHAR(500)");
这里有几个问题：
你永远不会在第一个PQexec的结果上调用PQclear，这会留下内存泄漏。请记住，res包含一个指向动态分配的返回结构的指针。这就是valgrind所抱怨的。
您没有正确检查第一个查询的结果。只检查PGexec的返回值是否为null，没有说明执行命令的结果，它只确认libpq能够分配足够的内存来返回结果结构。
您也没有检查错误。您应该调用PQresultStatus来确定查询是否成功执行。
如果您确实检查了错误，我怀疑您会发现您正在尝试执行的SQL。 SQL中没有IF语句。 PL / pgSQL中有一个，但它位于存储过程的上下文中。
有关正确呼叫方式的详细信息，请参阅libpq文档。