I think I understand.
When I use this in my code I get
"undefined reference to `PQexecParms'
when compiling.
references in main is
const char *conninfo; /* connection string to the database */
PGconn *conn; /* connection to the database */
PGresult *res; /* result of sql query */
int nFields; /* print out the attribute names */
int i; / * print the columns */
j;
Is the a reserved reference to use with
Reserved res = PQexecParms(conn.... )
Then I assume that I have to use another reference than res.
Thanks.
/Poul
2016-11-22 0:48 GMT+01:00 John McKown <john.archie.mckown@xxxxxxxxx>:
Thank you for fast repons!The $1 substitution below. I assume that it refers to "joe's place". But it is not very clear to me, how "joe's place" will appear instead of $1 when running. Where is it possiible to read more about this? There just is'nt much about substitution in C online. Any recommended books to buy?/* Here is our out-of-line parameter value */paramValues[0] = "joe's place";res = PQexecParams(conn,"SELECT * FROM test1 WHERE t = $1",1, /* one param */NULL, /* let the backend deduce param type */paramValues,NULL, /* don't need param lengths since text */NULL, /* default to all text params */1); /* ask for binary results */}/PoulIt is described better here: https://www.postgresql.org/docs/9.6/static/libpq-exec. html than I can do. But I just noticed a mistake in your code, or maybe just something left out. I would say:char *value1 = "joe's place";char **paramValues = &value1; /* closer match to the documentation's syntax *///char *paramValues[] = {"joe's place"}; /* same as above, different syntax */////char *paramValues[1]; /* this looks to be missing *///paramValues[0]="joe's place"; /* what you had */res = PQexecParms(conn,"SELECT * FROM test1 WHERE t = $1",1, /* there is only 1 entry in paramValues array */paramValues, /* address of parameter value array */NULL, /* don't need param lengths since text */NULL, /* defaul to all text params */1); /* return all values as binary */Well, you have an array of pointers to characters called paramValues. The $1 refers to whatever is pointed to by paramValues[0], which is a pointer to value1 which is a C "string". Basically in the second parameter, the command, the $n is used as a 1-based index into the paramValues[] array. This means that the actual C language array value is one less (since C arrays are 0-based). Which means that "$n" (n>=1) in the "command" string refers to value pointed to by paramValues[n-1]. The 3rd value, 1 in this case, tells PQexecParms how many entries there are in the paramValues[] array. I guess this is a type of validity check that the $n in the command string is not too large for the array.Note: please keep the discussion on the list, not to me personally. It may be of help to others (or maybe not, I don't know.)--Maranatha! <><
John McKown
Med venlig hilsen / Best regards
Poul Kristensen
Linux-OS/Virtualizationexpert and Oracle DBA
Poul Kristensen
Linux-OS/Virtualizationexpert and Oracle DBA
