Concatenate C string for postgresql

Question

So I'm trying to build my sql statement in the for loop.
But on executing, it shows error at the very first point of the string.
Is the concatenation method wrong, cause I printed the sql statement and manually execute in postgresql and it works.

Also I had tried

char *sqlStatement = "INSERT INTO record()..VALUES();\
    INSERT INTO record()..VALUES();\
    INSERT INTO record()..VALUES();
"

That works.

Note that I have reduced the loop to only once and reduced the number of columns for brevity.

The code:

char sqlStatement[8000];
for(int i=0;i<1;i++) {
        sprintf(&sqlStatement[0] + strlen(sqlStatement), "INSERT INTO record (\"user_id\", \"filename\", \"ports\", \"timestamp\" ... )VALUES (1, 'example%d', 0, '123456789%d', ... );", i, i,);
}
pgResult = PQexec(pgConn, sqlStatement);
if (PQresultStatus(pgResult) != PGRES_COMMAND_OK) {
        printf("%s", PQresultErrorMessage(pgResult));
        PQclear(pgResult);
        closeSQL(pgConn);
        exit(-1);
}

Error message:

ERROR:  syntax error at or near ""
LINE 1: INSERT INTO captures ("user_id", "filename", "ports", "time...        
        ^

melpomene · Accepted Answer · 2013-02-26 03:21:50Z

1

You're calling strlen(sqlStatement) but sqlStatement is uninitialized at that point. That's undefined behavior.

Put

sqlStatement[0] = '\0';

before the loop to start out with an empty string.

By the way, exit(-1) is wrong. The only standard C exit values are 0/EXIT_SUCCESS and EXIT_FAILURE. On Unix you can use any value between 0 and 255. I'm not sure about Windows but it's probably similar. I don't know any OS where -1 is valid.

answered Feb 26, 2013 at 3:21

melpomene

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1 Comment

resting Over a year ago

Ah...that solved my headache. Thanks! Will change the exit to the standard method too. :)

wildplasser · Accepted Answer · 2013-02-26 08:37:55Z

0

char sqlStatement[11111];
size_t_pos;

pos=0; 
pos += sprintf(sqlStatement+pos, "INSERT INTO record() VALUES(%s);\n" , "Argh!" );
pos += sprintf(sqlStatement+pos, "INSERT INTO record(...);\n" ... );
pos += sprintf(sqlStatement+pos, "INSERT INTO record(...);\n" ... );
...

A real program should of course first check the return value from sprintf, before using it to increment the pos position.

answered Feb 26, 2013 at 8:37

wildplasser

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