Data types and structures

C types are used to write C-Extensions.

The following C types are used to write C-Extensions.

Table 1. C types used to write C-Extensions
Type name Description
bigint signed integer with a size of 8 bytes
int4 signed integer with a size of 4 bytes
uint4 unsigned integer with a size of 4 bytes
int2 signed integer with a size of 2 bytes
uint2 unsigned integer with a size of 2 bytes
int1 signed integer with a size of 1 byte
uint1 unsigned integer with a size of 1 byte
mint signed machine-dependent C int
muint unsigned machine-dependent C int
mlong signed machine-dependent C long
mulong unsigned machine-dependent C long
dec_t DECIMAL data type structure
dtime_t DATETIME data type structure
intrvl_t INTERVAL data type structure
ifx_loc_t TEXT / BYTE locator structure

Basic data types

Basic data types such as bigint, int4 and int2 are provided to define variables that must hold BIGINT (bigint), SMALLINT (int2), INTEGER (int4) and DATE (int4) values. Standard char array can be used to hold CHAR and VARCHAR data.


No specific typedef exists for the DATE type; you can use the int4 type to store a DATE value.


The dec_t structure is provided to hold DECIMAL and MONEY values.

The internals of dec_t structure can be ignored during C-Extension programming, because decimal API functions are provided to manipulate any aspects of a decimal.


The dtime_t structure holds a DATETIME value.

Before manipulating a dtime_t, you must initialize its qualifier qt_qual, by using the TU_DTENCODE macro:

dtime_t dt;
dtcvasc( "2004-02-12 12:34:56", &dt );


The intrvl_t structure holds an INTERVAL value.

Before manipulating an intrvl_t, you must initialize its qualifier in_qual, by using the TU_IENCODE macro:

intrvl_t in;
in.in_qual = TU_IENCODE(5, TU_YEAR, TU_MONTH);
incvasc( "65234-02", &in );


The ifx_loc_t structure is used to declare host variables for a TEXT/BYTE values (simple large objects). Because the potential size of the data can be quite large, this is a locator structure that contains information about the size and location of the TEXT/BYTE data, rather than containing the actual data.

Table 2. Fields of the ifx_loc_t structure
Field name Data type Description
loc_indicator int4 Null indicator; a value of -1 indicates a null TEXT/BYTE value. Your program can set the field to indicate the insertion of a null value. Database client libraries set the value for selects and fetches.
loc_type int4 data type - SQLTEXT (for TEXT values) or SQLBYTES (for BYTE values).
loc_size int4 Size of the TEXT/BYTE value in bytes; your program sets the size of the large object for insertions. Database client libraries set the size for selects and fetches.
loc_loctype int2 Location - LOCMEMORY (in memory) or LOCFNAME (in a named file). Set loc_loctype after you declare the locator variable and before this declared variable receives the large object value.
loc_buffer char * If loc_loctype is LOCMEMORY, this is the location of the TEXT/BYTE value; your program must allocate space for the buffer and store its address here.
loc_bufsize int4 If loc_loctype is LOCMEMORY, this is the size of the buffer loc_buffer; If you set loc_bufsize to -1, database client libraries will allocate the memory buffer for selects and fetches. Otherwise, it is assumed that your program will handle memory allocation and de-allocation.
loc_fname char * If loc_loc_type is LOCFNAME, this is the address of the path name string that contains the file.


C Extension source (ext1.c):
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include "f2c/fglExt.h"

int lob_size(int);

UsrFunction usrFunctions[]={
  { "lob_size",     lob_size,       1, 1 },
  { NULL,           NULL,           0, 0 }

int lob_size(int pc)
    ifx_loc_t *pb1;
    double ratio;
    char *source = NULL;
    char *psource = NULL;
    int size;

    if (pc != 1) exit(1);

    if (pb1->loc_loctype == LOCMEMORY) {
        psource = pb1->loc_buffer;
        size = pb1->loc_size;
    } else if (pb1->loc_loctype == LOCFNAME) {
        int fd;
        struct stat st;
        fd = open(pb1->loc_fname, O_RDONLY);
        fstat(fd, &st);
        size = st.st_size;
        psource = source = (char *) malloc(size);
        read(fd, source, size);
    return 1;

Genero program (main.4gl):

IMPORT libext1
    LET t = "aaaaaaaaaaaaaa"
    DISPLAY lob_size(t)
Commands to compile and execute (on Linux):
$ gcc -fPIC -c ext1.c -I $FGLDIR/include
$ gcc --shared -o ext1.o -L$FGLDIR/lib -lfgl
$ fglcomp main.4gl
$ fglrun main.42m