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 */}/Poul
It 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 **paramVa
lues = &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
John McKown
