PQputvf (3)

#include <libpqtypes.h>

int PQputf(PGparam *param, const char *format, ...);

int PQputvf(PGparam *param, char *stmtBuf, size_t stmtBufLen,

            const char *format, va_list ap);

The PQputf() and PQputvf() functions put one or more query parameters into a PGparam using a printf style interface. Any number of parameters can be put at the same time.

The format argument is a data type specifier string indicating the parameters being put, such as "%int4 %polygon". format cannot be NULL or an empty string. The variable argument list must match the format, either "..." or ap. The number of arguments required for each data type is dependant on the data type itself; built-in PostgreSQL types always require a single argument.

The PQputvf() function can construct a parameterized command string from format, as long as stmtBuf and stmtBufLen have been provided. If the construction of stmtBuf is not desired, set it to NULL and set stmtBufLen to 0. When a constructed statement is desired, the contents of format will be copied to stmtBuf and all data type specifiers, like "%int4", will be replaced with $1, $2, etc... syntax. The result is a parameterized statement in synch with param and ready to be executed. For instance: if spec is "SELECT %int4 + %int4", the resulting stmtBuf would be "SELECT $1 + $2".

On success, a non-zero value is returned. On error, zero is returned and PQgeterror(3) will contain an error message.

If any put operation fails, the param is reverted back to the number of parameters it had prior to the function call; partial puts are not allowed.

Using PQputf

The example uses PQputf() to put a couple parameters into a PGparam.

PGtext text = "foobar";
PGint8 i8 = PQT_INT64CONST(1099511627776);
PGparam *param = PQparamCreate(conn);

if(!PQputf(param, "%text %int8", text, i8))
	fprintf(stderr, "*ERROR: %s\n", PQgeterror());

PQparamClear(param);

Using PQputvf

The example creates an application function named execf. execf is a wrapper to PQputvf(), as well as PQparamExec(3). It is similar to PQexecf(). The only difference is that the PQexecf implementation uses a smaller stack buffer and allocates heap memory when needed.

PGresult *
execf(PGconn *conn, const char *format, ...)
{
	va_list ap;
	char stmt[32768];
	PGparam *param;
	PGresult *res = NULL;

	/* create the temporary PGparam */
	if(!(param = PQparamCreate(conn)))
		return NULL; /* PQseterror already called */

	/* put the params, create the stmt and exec it */
	va_start(ap, format);
	if(PQputvf(param, stmt, sizeof(stmt), format, ap))
		res = PQparamExec(conn, param, stmt, 1); // resfmt is binary
	va_end(ap);

	/* param must be cleared */
	PQparamClear(param);
	return res;
}

/* Example: execf will put 2 ints and execute "SELECT $1 + $2" */
PGresult *res = execf(conn, "SELECT %int4 + %int4", 100, 67);
if(!res)
	fprintf(stderr, "*ERROR: %s\n", PQgeterror());

A contribution of eSilo, LLC. for the PostgreSQL Database Management System. Written by Andrew Chernow and Merlin Moncure.

Report bugs to <[email protected]>.

Copyright (c) 2011 eSilo, LLC. All rights reserved.

This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

pqt-specs(3), PQparamCreate(3), PQgeterror(3), PQseterror(3)