postgres.h

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/*-------------------------------------------------------------------------
 *
 * postgres.h
 *    Primary include file for PostgreSQL server .c files
 *
 * This should be the first file included by PostgreSQL backend modules.
 * Client-side code should include postgres_fe.h instead.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1995, Regents of the University of California
 *
 * src/include/postgres.h
 *
 *-------------------------------------------------------------------------
 */
/* IWYU pragma: always_keep */
/*
 *----------------------------------------------------------------
 *   TABLE OF CONTENTS
 *
 *      When adding stuff to this file, please try to put stuff
 *      into the relevant section, or add new sections as appropriate.
 *
 *    section   description
 *    -------   ------------------------------------------------
 *      1)      Datum type + support functions
 *      2)      miscellaneous
 *
 *   NOTES
 *
 *  In general, this file should contain declarations that are widely needed
 *  in the backend environment, but are of no interest outside the backend.
 *
 *  Simple type definitions live in c.h, where they are shared with
 *  postgres_fe.h.  We do that since those type definitions are needed by
 *  frontend modules that want to deal with binary data transmission to or
 *  from the backend.  Type definitions in this file should be for
 *  representations that never escape the backend, such as Datum.
 *
 *----------------------------------------------------------------
 */
#ifndef POSTGRES_H
#define POSTGRES_H
 
/* IWYU pragma: begin_exports */
 
#include "c.h"
#include "utils/elog.h"
#include "utils/palloc.h"
 
/* IWYU pragma: end_exports */
 
/* ----------------------------------------------------------------
 *              Section 1:  Datum type + support functions
 * ----------------------------------------------------------------
 */
 
/*
 * A Datum contains either a value of a pass-by-value type or a pointer to a
 * value of a pass-by-reference type.  Therefore, we must have
 * sizeof(Datum) >= sizeof(void *).  No current or foreseeable Postgres
 * platform has pointers wider than 8 bytes, and standardizing on Datum being
 * exactly 8 bytes has advantages in reducing cross-platform differences.
 *
 * The functions below and the analogous functions for other types should be used to
 * convert between a Datum and the appropriate C type.
 */
 
typedef uint64_t Datum;
 
/*
 * This symbol is now vestigial, but we continue to define it so as not to
 * unnecessarily break extension code.
 */
#define SIZEOF_DATUM 8
 
/*
 * A NullableDatum is used in places where both a Datum and its nullness needs
 * to be stored. This can be more efficient than storing datums and nullness
 * in separate arrays, due to better spatial locality, even if more space may
 * be wasted due to padding.
 */
typedef struct NullableDatum
{
#define FIELDNO_NULLABLE_DATUM_DATUM 0
    Datum       value;
#define FIELDNO_NULLABLE_DATUM_ISNULL 1
    bool        isnull;
    /* due to alignment padding this could be used for flags for free */
} NullableDatum;
 
/*
 * DatumGetBool
 *      Returns boolean value of a datum.
 *
 * Note: any nonzero value will be considered true.
 */
static inline bool
DatumGetBool(Datum X)
{
    return (X != 0);
}
 
/*
 * BoolGetDatum
 *      Returns datum representation for a boolean.
 *
 * Note: any nonzero value will be considered true.
 */
static inline Datum
BoolGetDatum(bool X)
{
    return (Datum) (X ? 1 : 0);
}
 
/*
 * DatumGetChar
 *      Returns character value of a datum.
 */
static inline char
DatumGetChar(Datum X)
{
    return (char) X;
}
 
/*
 * CharGetDatum
 *      Returns datum representation for a character.
 */
static inline Datum
CharGetDatum(char X)
{
    return (Datum) X;
}
 
/*
 * DatumGetUInt8
 *      Returns 8-bit unsigned integer value of a datum.
 */
static inline uint8
DatumGetUInt8(Datum X)
{
    return (uint8) X;
}
 
/*
 * UInt8GetDatum
 *      Returns datum representation for an 8-bit unsigned integer.
 */
static inline Datum
UInt8GetDatum(uint8 X)
{
    return (Datum) X;
}
 
/*
 * DatumGetInt16
 *      Returns 16-bit integer value of a datum.
 */
static inline int16
DatumGetInt16(Datum X)
{
    return (int16) X;
}
 
/*
 * Int16GetDatum
 *      Returns datum representation for a 16-bit integer.
 */
static inline Datum
Int16GetDatum(int16 X)
{
    return (Datum) X;
}
 
/*
 * DatumGetUInt16
 *      Returns 16-bit unsigned integer value of a datum.
 */
static inline uint16
DatumGetUInt16(Datum X)
{
    return (uint16) X;
}
 
/*
 * UInt16GetDatum
 *      Returns datum representation for a 16-bit unsigned integer.
 */
static inline Datum
UInt16GetDatum(uint16 X)
{
    return (Datum) X;
}
 
/*
 * DatumGetInt32
 *      Returns 32-bit integer value of a datum.
 */
static inline int32
DatumGetInt32(Datum X)
{
    return (int32) X;
}
 
/*
 * Int32GetDatum
 *      Returns datum representation for a 32-bit integer.
 */
static inline Datum
Int32GetDatum(int32 X)
{
    return (Datum) X;
}
 
/*
 * DatumGetUInt32
 *      Returns 32-bit unsigned integer value of a datum.
 */
static inline uint32
DatumGetUInt32(Datum X)
{
    return (uint32) X;
}
 
/*
 * UInt32GetDatum
 *      Returns datum representation for a 32-bit unsigned integer.
 */
static inline Datum
UInt32GetDatum(uint32 X)
{
    return (Datum) X;
}
 
/*
 * DatumGetObjectId
 *      Returns object identifier value of a datum.
 */
static inline Oid
DatumGetObjectId(Datum X)
{
    return (Oid) X;
}
 
/*
 * ObjectIdGetDatum
 *      Returns datum representation for an object identifier.
 */
static inline Datum
ObjectIdGetDatum(Oid X)
{
    return (Datum) X;
}
 
/*
 * DatumGetObjectId8
 *      Returns 8-byte object identifier value of a datum.
 */
static inline Oid8
DatumGetObjectId8(Datum X)
{
    return (Oid8) X;
}
 
/*
 * ObjectId8GetDatum
 *      Returns datum representation for an 8-byte object identifier
 */
static inline Datum
ObjectId8GetDatum(Oid8 X)
{
    return (Datum) X;
}
 
/*
 * DatumGetTransactionId
 *      Returns transaction identifier value of a datum.
 */
static inline TransactionId
DatumGetTransactionId(Datum X)
{
    return (TransactionId) X;
}
 
/*
 * TransactionIdGetDatum
 *      Returns datum representation for a transaction identifier.
 */
static inline Datum
TransactionIdGetDatum(TransactionId X)
{
    return (Datum) X;
}
 
/*
 * MultiXactIdGetDatum
 *      Returns datum representation for a multixact identifier.
 */
static inline Datum
MultiXactIdGetDatum(MultiXactId X)
{
    return (Datum) X;
}
 
/*
 * DatumGetCommandId
 *      Returns command identifier value of a datum.
 */
static inline CommandId
DatumGetCommandId(Datum X)
{
    return (CommandId) X;
}
 
/*
 * CommandIdGetDatum
 *      Returns datum representation for a command identifier.
 */
static inline Datum
CommandIdGetDatum(CommandId X)
{
    return (Datum) X;
}
 
/*
 * DatumGetPointer
 *      Returns pointer value of a datum.
 */
static inline Pointer
DatumGetPointer(Datum X)
{
    return (Pointer) (uintptr_t) X;
}
 
/*
 * PointerGetDatum
 *      Returns datum representation for a pointer.
 *
 * This used to be defined as "static inline Datum PointerGetDatum(const void
 * *X) ", but it had the problem that the compiler would see the const
 * attribute, and could rightly assume that the function won't modify *X.
 * While PointerGetDatum() itself doesn't modify *X, the resulting Datum could
 * later be passed to a function that converts it back to a non-const pointer
 * and modifies it.  Most functions don't modify their arguments passed by
 * reference - that would be very bogus for any operators or functions exposed
 * in SQL - but some functions like GIN support functions do have output
 * arguments that are pointer Datums.
 *
 * The odd-looking "true ? (X) : NULL" conditional expression has the effect
 * of producing a compiler error if X is not a pointer.
 */
#define PointerGetDatum(X) \
    ((Datum) (uintptr_t) (true ? (X) : NULL))
 
/*
 * DatumGetCString
 *      Returns C string (null-terminated string) value of a datum.
 *
 * Note: C string is not a full-fledged Postgres type at present,
 * but type input functions use this conversion for their inputs.
 */
static inline char *
DatumGetCString(Datum X)
{
    return (char *) DatumGetPointer(X);
}
 
/*
 * CStringGetDatum
 *      Returns datum representation for a C string (null-terminated string).
 *
 * We assume that the resulting Datum is not used to modify the string, hence
 * the argument can be marked as const.
 *
 * Note: C string is not a full-fledged Postgres type at present,
 * but type output functions use this conversion for their outputs.
 * Note: CString is pass-by-reference; caller must ensure the pointed-to
 * value has adequate lifetime.
 */
static inline Datum
CStringGetDatum(const char *X)
{
    return PointerGetDatum(X);
}
 
/*
 * DatumGetName
 *      Returns name value of a datum.
 */
static inline Name
DatumGetName(Datum X)
{
    return (Name) DatumGetPointer(X);
}
 
/*
 * NameGetDatum
 *      Returns datum representation for a name.
 *
 * Note: Name is pass-by-reference; caller must ensure the pointed-to
 * value has adequate lifetime.
 */
static inline Datum
NameGetDatum(const NameData *X)
{
    return CStringGetDatum(NameStr(*X));
}
 
/*
 * DatumGetInt64
 *      Returns 64-bit integer value of a datum.
 */
static inline int64
DatumGetInt64(Datum X)
{
    return (int64) X;
}
 
/*
 * Int64GetDatum
 *      Returns datum representation for a 64-bit integer.
 */
static inline Datum
Int64GetDatum(int64 X)
{
    return (Datum) X;
}
 
/*
 * DatumGetUInt64
 *      Returns 64-bit unsigned integer value of a datum.
 */
static inline uint64
DatumGetUInt64(Datum X)
{
    return (uint64) X;
}
 
/*
 * UInt64GetDatum
 *      Returns datum representation for a 64-bit unsigned integer.
 */
static inline Datum
UInt64GetDatum(uint64 X)
{
    return (Datum) X;
}
 
/*
 * Float <-> Datum conversions
 *
 * These have to be implemented as inline functions rather than macros, when
 * passing by value, because many machines pass int and float function
 * parameters/results differently; so we need to play weird games with unions.
 */
 
/*
 * DatumGetFloat4
 *      Returns 4-byte floating point value of a datum.
 */
static inline float4
DatumGetFloat4(Datum X)
{
    union
    {
        int32       value;
        float4      retval;
    }           myunion;
 
    myunion.value = DatumGetInt32(X);
    return myunion.retval;
}
 
/*
 * Float4GetDatum
 *      Returns datum representation for a 4-byte floating point number.
 */
static inline Datum
Float4GetDatum(float4 X)
{
    union
    {
        float4      value;
        int32       retval;
    }           myunion;
 
    myunion.value = X;
    return Int32GetDatum(myunion.retval);
}
 
/*
 * DatumGetFloat8
 *      Returns 8-byte floating point value of a datum.
 */
static inline float8
DatumGetFloat8(Datum X)
{
    union
    {
        int64       value;
        float8      retval;
    }           myunion;
 
    myunion.value = DatumGetInt64(X);
    return myunion.retval;
}
 
/*
 * Float8GetDatum
 *      Returns datum representation for an 8-byte floating point number.
 */
static inline Datum
Float8GetDatum(float8 X)
{
    union
    {
        float8      value;
        int64       retval;
    }           myunion;
 
    myunion.value = X;
    return Int64GetDatum(myunion.retval);
}
 
/*
 * Int64GetDatumFast
 * Float8GetDatumFast
 *
 * These macros were intended to allow writing code that does not depend on
 * whether int64 and float8 are pass-by-reference types, while not
 * sacrificing performance when they are.  They are no longer different
 * from the regular functions, though we keep the assertions to protect
 * code that might get back-patched into older branches.
 */
 
#define Int64GetDatumFast(X) \
    (StaticAssertVariableIsOfTypeMacro(X, int64), Int64GetDatum(X))
#define Float8GetDatumFast(X) \
    (StaticAssertVariableIsOfTypeMacro(X, double), Float8GetDatum(X))
 
 
/* ----------------------------------------------------------------
 *              Section 2:  miscellaneous
 * ----------------------------------------------------------------
 */
 
/*
 * pg_ternary
 *      Boolean value with an extra "unset" value
 *
 * This enum can be used for values that want to distinguish between true,
 * false, and unset.
*/
typedef enum pg_ternary
{
    PG_TERNARY_FALSE = 0,
    PG_TERNARY_TRUE = 1,
    PG_TERNARY_UNSET = -1
} pg_ternary;
 
/*
 * NON_EXEC_STATIC: It's sometimes useful to define a variable or function
 * that is normally static but extern when using EXEC_BACKEND (see
 * pg_config_manual.h).  There would then typically be some code in
 * postmaster.c that uses those extern symbols to transfer state between
 * processes or do whatever other things it needs to do in EXEC_BACKEND mode.
 */
#ifdef EXEC_BACKEND
#define NON_EXEC_STATIC
#else
#define NON_EXEC_STATIC static
#endif
 
#endif                          /* POSTGRES_H */