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Frees memory allocated bylibpq.

void PQfreemem(void *ptr);

Frees memory allocated bylibpq, particularlyPQescapeByteaConn,PQescapeBytea,PQunescapeBytea, andPQnotifies. It is particularly important that this function, rather thanfree(), be used on Microsoft Windows. This is because allocating memory in a DLL and releasing it in the application works only if multithreaded/single-threaded, release/debug, and static/dynamic flags are the same for the DLL and the application. On non-Microsoft Windows platforms, this function is the same as the standard library functionfree().

Frees the data structures allocated byPQconndefaults orPQconninfoParse.

void PQconninfoFree(PQconninfoOption *connOptions);

If the argument is aNULL pointer, no operation is performed.

A simplePQfreemem will not do for this, since the array contains references to subsidiary strings.

Prepares the encrypted form of aPostgreSQL password.

char *PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user, const char *algorithm);

This function is intended to be used by client applications that wish to send commands likeALTER USER joe PASSWORD 'pwd'. It is good practice not to send the original cleartext password in such a command, because it might be exposed in command logs, activity displays, and so on. Instead, use this function to convert the password to encrypted form before it is sent.

Thepasswd anduser arguments are the cleartext password, and the SQL name of the user it is for.algorithm specifies the encryption algorithm to use to encrypt the password. Currently supported algorithms aremd5 andscram-sha-256 (on andoff are also accepted as aliases formd5, for compatibility with older server versions). Note that support forscram-sha-256 was introduced inPostgreSQL version 10, and will not work correctly with older server versions. Ifalgorithm isNULL, this function will query the server for the current value of thepassword_encryption setting. That can block, and will fail if the current transaction is aborted, or if the connection is busy executing another query. If you wish to use the default algorithm for the server but want to avoid blocking, querypassword_encryption yourself before callingPQencryptPasswordConn, and pass that value as thealgorithm.

The return value is a string allocated bymalloc. The caller can assume the string doesn't contain any special characters that would require escaping. UsePQfreemem to free the result when done with it. On error, returnsNULL, and a suitable message is stored in the connection object.

Changes aPostgreSQL password.

PGresult *PQchangePassword(PGconn *conn, const char *user, const char *passwd);

This function usesPQencryptPasswordConn to build and execute the commandALTER USER ... PASSWORD '...', thereby changing the user's password. It exists for the same reason asPQencryptPasswordConn, but is more convenient as it both builds and runs the command for you.PQencryptPasswordConn is passed aNULL for the algorithm argument, hence encryption is done according to the server'spassword_encryption setting.

Theuser andpasswd arguments are the SQL name of the target user, and the new cleartext password.

Returns aPGresult pointer representing the result of theALTER USER command, or a null pointer if the routine failed before issuing any command. ThePQresultStatus function should be called to check the return value for any errors (including the value of a null pointer, in which case it will returnPGRES_FATAL_ERROR). UsePQerrorMessage to get more information about such errors.

Prepares the md5-encrypted form of aPostgreSQL password.

char *PQencryptPassword(const char *passwd, const char *user);

PQencryptPassword is an older, deprecated version ofPQencryptPasswordConn. The difference is thatPQencryptPassword does not require a connection object, andmd5 is always used as the encryption algorithm.

Constructs an emptyPGresult object with the given status.

PGresult *PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status);

This islibpq's internal function to allocate and initialize an emptyPGresult object. This function returnsNULL if memory could not be allocated. It is exported because some applications find it useful to generate result objects (particularly objects with error status) themselves. Ifconn is not null andstatus indicates an error, the current error message of the specified connection is copied into thePGresult. Also, ifconn is not null, any event procedures registered in the connection are copied into thePGresult. (They do not getPGEVT_RESULTCREATE calls, but seePQfireResultCreateEvents.) Note thatPQclear should eventually be called on the object, just as with aPGresult returned bylibpq itself.

Fires aPGEVT_RESULTCREATE event (seeSection 32.14) for each event procedure registered in thePGresult object. Returns non-zero for success, zero if any event procedure fails.

int PQfireResultCreateEvents(PGconn *conn, PGresult *res);

Theconn argument is passed through to event procedures but not used directly. It can beNULL if the event procedures won't use it.

Event procedures that have already received aPGEVT_RESULTCREATE orPGEVT_RESULTCOPY event for this object are not fired again.

The main reason that this function is separate fromPQmakeEmptyPGresult is that it is often appropriate to create aPGresult and fill it with data before invoking the event procedures.

Makes a copy of aPGresult object. The copy is not linked to the source result in any way andPQclear must be called when the copy is no longer needed. If the function fails,NULL is returned.

PGresult *PQcopyResult(const PGresult *src, int flags);

This is not intended to make an exact copy. The returned result is always put intoPGRES_TUPLES_OK status, and does not copy any error message in the source. (It does copy the command status string, however.) Theflags argument determines what else is copied. It is a bitwise OR of several flags.PG_COPYRES_ATTRS specifies copying the source result's attributes (column definitions).PG_COPYRES_TUPLES specifies copying the source result's tuples. (This implies copying the attributes, too.)PG_COPYRES_NOTICEHOOKS specifies copying the source result's notify hooks.PG_COPYRES_EVENTS specifies copying the source result's events. (But any instance data associated with the source is not copied.) The event procedures receivePGEVT_RESULTCOPY events.

Sets the attributes of aPGresult object.

int PQsetResultAttrs(PGresult *res, int numAttributes, PGresAttDesc *attDescs);

The providedattDescs are copied into the result. If theattDescs pointer isNULL ornumAttributes is less than one, the request is ignored and the function succeeds. Ifres already contains attributes, the function will fail. If the function fails, the return value is zero. If the function succeeds, the return value is non-zero.

Sets a tuple field value of aPGresult object.

int PQsetvalue(PGresult *res, int tup_num, int field_num, char *value, int len);

The function will automatically grow the result's internal tuples array as needed. However, thetup_num argument must be less than or equal toPQntuples, meaning this function can only grow the tuples array one tuple at a time. But any field of any existing tuple can be modified in any order. If a value atfield_num already exists, it will be overwritten. Iflen is -1 orvalue isNULL, the field value will be set to an SQL null value. Thevalue is copied into the result's private storage, thus is no longer needed after the function returns. If the function fails, the return value is zero. If the function succeeds, the return value is non-zero.

Allocate subsidiary storage for aPGresult object.

void *PQresultAlloc(PGresult *res, size_t nBytes);

Any memory allocated with this function will be freed whenres is cleared. If the function fails, the return value isNULL. The result is guaranteed to be adequately aligned for any type of data, just as formalloc.

Retrieves the number of bytes allocated for aPGresult object.

size_t PQresultMemorySize(const PGresult *res);

This value is the sum of allmalloc requests associated with thePGresult object, that is, all the memory that will be freed byPQclear. This information can be useful for managing memory consumption.

Return the version oflibpq that is being used.

int PQlibVersion(void);

The result of this function can be used to determine, at run time, whether specific functionality is available in the currently loaded version of libpq. The function can be used, for example, to determine which connection options are available inPQconnectdb.

The result is formed by multiplying the library's major version number by 10000 and adding the minor version number. For example, version 10.1 will be returned as 100001, and version 11.0 will be returned as 110000.

Prior to major version 10,PostgreSQL used three-part version numbers in which the first two parts together represented the major version. For those versions,PQlibVersion uses two digits for each part; for example version 9.1.5 will be returned as 90105, and version 9.2.0 will be returned as 90200.

Therefore, for purposes of determining feature compatibility, applications should divide the result ofPQlibVersion by 100 not 10000 to determine a logical major version number. In all release series, only the last two digits differ between minor releases (bug-fix releases).

Retrieves the current time, expressed as the number of microseconds since the Unix epoch (that is,time_t times 1 million).

pg_usec_time_t PQgetCurrentTimeUSec(void);

This is primarily useful for calculating timeout values to use withPQsocketPoll.