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Examples
Updated on 2025-08-19 GMT+08:00
Examples
ecpg Example Code
#include <locale.h>
#include <string.h>
#include <stdlib.h>
exec sql whenever sqlerror sqlprint;
exec sql include sqlca;
int main(void)
{
EXEC SQL BEGIN DECLARE SECTION;
char *temp_str = (char *)malloc(11);
EXEC SQL END DECLARE SECTION;
ECPGdebug(1, stderr);
exec sql connect to postgres;
/* Enable the automatic commit function. You do not need to manually commit the exec sql command. */
exec sql set autocommit = on;
exec sql drop table if exists test_t;
/* Create a table and insert data. */
exec sql create table test_t(f float, i int, a int[10], mstr char(10));
exec sql insert into test_t(f, i, a, mstr) values(1.01,1,'{0,1,2,3,4,5,6,7,8,9}', 'China');
/* Disable the automatic commit function. The following SQL statements for inserting data must be manually committed: */
exec sql set autocommit = off;
exec sql insert into test_t(f, i, a, mstr) values(2.01,2,'{0,1,2,3,4,5,6,7,8,9}', 'USA');
exec sql commit;
exec sql insert into test_t(f, i, a, mstr) values(3.01,3,'{0,1,2,3,4,5,6,7,8,9}', 'AUS');
exec sql insert into test_t(f, i, a, mstr) values(4.01,4,'{0,1,2,3,4,5,6,7,8,9}', 'JAP');
exec sql commit;
EXEC SQL BEGIN DECLARE SECTION;
int a[10] = {9,8,7,6,5,4,3,2,1,0};
int id = 6;
EXEC SQL END DECLARE SECTION;
/* Fetch data from the host variable and insert the data into the table. The type of the host variable is the same as that defined in the table. */
strcpy(temp_str, "RUS");
exec sql insert into test_t(f, i, a, mstr) values(5.01,5,:a,:temp_str);
exec sql commit;
exec sql set autocommit = on;
exec sql begin;
exec sql insert into test_t(f, i, a, mstr) values(6.01,:id,:a,'SIG');
exec sql commit;
exec sql set autocommit = off;
exec sql begin declare section;
float ff;
char tmp_text[25] = "klmnopqrst";
exec sql end declare section;
exec sql set autocommit = on;
exec sql begin work;
printf("Found ff=%f tmp_text=%10.10s\n", ff, tmp_text);
/* Example of a conditional query statement */
exec sql select f, mstr into :ff,:tmp_text from test_t where f > (select f from test_t where i = 4 or i < 0) order by a limit 1;
printf("Found ff=%f tmp_text=%10.10s\n", ff, tmp_text);
exec sql select f, mstr into :ff,:tmp_text from test_t where mstr = 'JAP' order by i;
printf("Found ff=%f tmp_text=%10.10s\n", ff, tmp_text);
exec sql select f, mstr into :ff,:tmp_text from test_t order by i DESC limit 1;
printf("Found ff=%f tmp_text=%10.10s\n", ff, tmp_text);
exec sql select f, mstr into :ff,:tmp_text from test_t order by mstr limit 1;
printf("Found ff=%f tmp_text=%10.10s\n", ff, tmp_text);
exec sql select count(f), a into :ff,:tmp_text from test_t where i > 2 group by a limit 1;
printf("Found ff=%f tmp_text=%20.30s\n", ff, tmp_text);
exec sql select count(f), a into :ff,:tmp_text from test_t where i > 3 group by a order by a limit 1;
printf("Found ff=%f tmp_text=%20.30s\n", ff, tmp_text);
exec sql select sum(f), a into :ff,:tmp_text from test_t where i > 2 group by a order by a limit 1;
printf("Found ff=%f tmp_text=%20.30s\n", ff, tmp_text);
exec sql select distinct a into :tmp_text from test_t order by a limit 1;
exec sql drop table test_t;
exec sql commit;
/* Release the connection and release the memory allocated to the host variable. */
exec sql disconnect;
free(temp_str);
return 0;
}
Example Code of the pgtypes Library Function
Example 1: Use library functions to perform different operations on time and date types. For details, see Using Library Functions.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <limits.h>
#include <pgtypes_date.h>
#include <pgtypes_timestamp.h>
char *dates[] = { "19990108foobar",
"19990108 foobar",
"1999-01-08 foobar",
"January 8, 1999",
"1999-01-08",
"1/8/1999",
"1/18/1999",
"01/02/03",
"1999-Jan-08",
"Jan-08-1999",
"08-Jan-1999",
"99-Jan-08",
"08-Jan-99",
"08-Jan-06",
"Jan-08-99",
"19990108",
"990108",
"1999.008",
"J2451187",
"January 8, 99 BC",
NULL
};
/* The value cannot conflict with the value of times of libc. */
static char *times[] = { "0:04",
"1:59 PDT",
"13:24:40 -8:00",
"13:24:40.495+3",
NULL
};
char *intervals[] = { "1 minute",
"1 12:59:10",
"2 day 12 hour 59 minute 10 second",
"1 days 12 hrs 59 mins 10 secs",
"1 days 1 hours 1 minutes 1 seconds",
"1 year 59 mins",
"1 year 59 mins foobar",
NULL
};
int main(void)
{
exec sql begin declare section;
date date1;
timestamp ts1, ts2;
char *text;
interval *i1;
date *dc;
exec sql end declare section;
int i, j;
char *endptr;
ECPGdebug(1, stderr);
/* Parse a timestamp from its textual representation and convert the date into a character string. */
ts1 = PGTYPEStimestamp_from_asc("2003-12-04 17:34:29", NULL);
text = PGTYPEStimestamp_to_asc(ts1);
printf("timestamp: %s\n", text);
free(text);
/* Extract the date part from the timestamp. */
date1 = PGTYPESdate_from_timestamp(ts1);
dc = PGTYPESdate_new();
*dc = date1;
/* Return the textual representation of a date variable. */
text = PGTYPESdate_to_asc(*dc);
printf("Date of timestamp: %s\n", text);
free(text);
PGTYPESdate_free(dc);
for (i = 0; dates[i]; i++)
{
bool err = false;
/* Parse a date from the textual representation of the date. */
date1 = PGTYPESdate_from_asc(dates[i], &endptr);
if (date1 == INT_MIN) {
err = true;
}
/* Return the textual representation of a date variable. */
text = PGTYPESdate_to_asc(date1);
printf("Date[%d]: %s (%c - %c)\n",
i, err ? "-" : text,
endptr ? 'N' : 'Y',
err ? 'T' : 'F');
free(text);
if (!err)
{
for (j = 0; times[j]; j++)
{
int length = strlen(dates[i])+ 1+ strlen(times[j])+ 1;
char* t = (char *)malloc(length);
sprintf(t, "%s %s", dates[i], times[j]);
/* Parse a timestamp from its textual representation and convert the date into a character string. */
ts1 = PGTYPEStimestamp_from_asc(t, NULL);
text = PGTYPEStimestamp_to_asc(ts1);
if (i != 19 || j != 3)
printf("TS[%d,%d]: %s\n",i, j, errno ? "-" : text);
free(text);
free(t);
}
}
}
/* Parse a timestamp from its textual representation. */
ts1 = PGTYPEStimestamp_from_asc("2004-04-04 23:23:23", NULL);
for (i = 0; intervals[i]; i++)
{
interval *ic;
/* Parse an interval from its textual representation. */
i1 = PGTYPESinterval_from_asc(intervals[i], &endptr);
if (*endptr)
printf("endptr set to %s\n", endptr);
if (!i1)
{
printf("Error parsing interval %d\n", i);
continue;
}
/* Add an interval variable to the timestamp variable. */
j = PGTYPEStimestamp_add_interval(&ts1, i1, &ts2);
if (j < 0)
continue;
/* Convert a variable of the interval type to the text format. */
text = PGTYPESinterval_to_asc(i1);
printf("interval[%d]: %s\n", i, text ? text : "-");
free(text);
/* Return a pointer to an allocated interval variable. */
ic = PGTYPESinterval_new();
/*Copy a variable of the interval type. */
PGTYPESinterval_copy(i1, ic);
/* Convert a variable of the interval type to the text format. */
text = PGTYPESinterval_to_asc(i1);
printf("interval_copy[%d]: %s\n", i, text ? text : "-");
free(text);
/* Release the memory that has been allocated to an interval variable. */
PGTYPESinterval_free(ic);
PGTYPESinterval_free(i1);
}
return (0);
}
Example 2: Use the pgtypes library function to perform different operations on the numeric type.
#include <stdio.h>
#include <stdlib.h>
#include <pgtypes_numeric.h>
#include <pgtypes_error.h>
#include <decimal.h>
char* nums[] = { "2E394", "-2", ".794", "3.44", "592.49E21", "-32.84e4",
"2E-394", ".1E-2", "+.0", "-592.49E-07", "+32.84e-4",
".500001", "-.5000001",
"1234567890123456789012345678.91", /* A 30-bit number should be converted into a decimal number.*/
"1234567890123456789012345678.921", /* A 31-bit number cannot be converted into a decimal number. */
"not a number",
NULL
};
static void check_errno(void);
int main(void)
{
char *text="error\n";
char *endptr;
numeric *num, *nin;
decimal *dec;
long l;
int i, j, k, q, r, count = 0;
double d;
numeric **numarr = (numeric **) calloc(1, sizeof(numeric));
ECPGdebug(1, stderr);
for (i = 0; nums[i]; i++)
{
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type nums[i]. */
num = PGTYPESnumeric_from_asc(nums[i], &endptr);
if (!num) check_errno();
if (endptr != NULL)
{
printf("endptr of %d is not NULL\n", i);
if (*endptr != '\0')
printf("*endptr of %d is not \\0\n", i);
}
if (!num) continue;
numarr = (numeric **)realloc(numarr, sizeof(numeric *) * (count + 1));
numarr[count++] = num;
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type num. */
text = PGTYPESnumeric_to_asc(num, -1);
if (!text) check_errno();
printf("num[%d,1]: %s\n", i, text); free(text);
text = PGTYPESnumeric_to_asc(num, 0);
if (!text) check_errno();
printf("num[%d,2]: %s\n", i, text); free(text);
text = PGTYPESnumeric_to_asc(num, 1);
if (!text) check_errno();
printf("num[%d,3]: %s\n", i, text); free(text);
text = PGTYPESnumeric_to_asc(num, 2);
if (!text) check_errno();
printf("num[%d,4]: %s\n", i, text); free(text);
/* Request a pointer to a newly allocated numeric variable. */
nin = PGTYPESnumeric_new();
text = PGTYPESnumeric_to_asc(nin, 2);
if (!text) check_errno();
printf("num[%d,5]: %s\n", i, text); free(text);
/* Convert a numeric variable into a long int variable. */
r = PGTYPESnumeric_to_long(num, &l);
if (r) check_errno();
printf("num[%d,6]: %ld (r: %d)\n", i, r?0L:l, r);
if (r == 0)
{
/* Convert a long int variable into a numeric variable. */
r = PGTYPESnumeric_from_long(l, nin);
if (r) check_errno();
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type nin. */
text = PGTYPESnumeric_to_asc(nin, 2);
/* Compare two numeric variables. */
q = PGTYPESnumeric_cmp(num, nin);
printf("num[%d,7]: %s (r: %d - cmp: %d)\n", i, text, r, q);
free(text);
}
/* Convert a numeric variable into an int variable. */
r = PGTYPESnumeric_to_int(num, &k);
if (r) check_errno();
printf("num[%d,8]: %d (r: %d)\n", i, r?0:k, r);
if (r == 0)
{
/* Convert an int variable into a numeric variable. */
r = PGTYPESnumeric_from_int(k, nin);
if (r) check_errno();
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type nin. */
text = PGTYPESnumeric_to_asc(nin, 2);
q = PGTYPESnumeric_cmp(num, nin);
printf("num[%d,9]: %s (r: %d - cmp: %d)\n", i, text, r, q);
free(text);
}
if (i != 6)
{
/* Convert a variable of the numeric type to the double-precision type. */
r = PGTYPESnumeric_to_double(num, &d);
if (r) check_errno();
printf("num[%d,10]: %g (r: %d)\n", i, r?0.0:d, r);
}
/* Request a pointer to a newly allocated numeric variable. */
dec = PGTYPESdecimal_new();
/* Convert a decimal variable into a numeric variable. */
r = PGTYPESnumeric_to_decimal(num, dec);
if (r) check_errno();
printf("num[%d,11]: - (r: %d)\n", i, r);
if (r == 0)
{
/* Convert a decimal variable into a numeric variable. */
r = PGTYPESnumeric_from_decimal(dec, nin);
if (r) check_errno();
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type nin. */
text = PGTYPESnumeric_to_asc(nin, 2);
/* Compare two numeric variables. */
q = PGTYPESnumeric_cmp(num, nin);
printf("num[%d,12]: %s (r: %d - cmp: %d)\n", i, text, r, q);
free(text);
}
/* Release the memory allocated to the numeric variable. */
PGTYPESdecimal_free(dec);
PGTYPESnumeric_free(nin);
printf("\n");
}
for (i = 0; i < count; i++)
{
for (j = 0; j < count; j++)
{
/* Request a pointer to a newly allocated numeric variable. */
numeric* a = PGTYPESnumeric_new();
numeric* s = PGTYPESnumeric_new();
numeric* m = PGTYPESnumeric_new();
numeric* d = PGTYPESnumeric_new();
/* Add two numeric variables to the third numeric variable. */
r = PGTYPESnumeric_add(numarr[i], numarr[j], a);
if (r)
{
check_errno();
printf("r: %d\n", r);
}
else
{
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type a. */
text = PGTYPESnumeric_to_asc(a, 10);
printf("num[a,%d,%d]: %s\n", i, j, text);
free(text);
}
/* Subtract two numeric variables and returns the result to the third numeric variable. */
r = PGTYPESnumeric_sub(numarr[i], numarr[j], s);
if (r)
{
check_errno();
printf("r: %d\n", r);
}
else
{
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type s. */
text = PGTYPESnumeric_to_asc(s, 10);
printf("num[s,%d,%d]: %s\n", i, j, text);
free(text);
}
/* Multiply two numeric variables and returns the result to the third numeric variable. */
r = PGTYPESnumeric_mul(numarr[i], numarr[j], m);
if (r)
{
check_errno();
printf("r: %d\n", r);
}
else
{
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type m. */
text = PGTYPESnumeric_to_asc(m, 10);
printf("num[m,%d,%d]: %s\n", i, j, text);
free(text);
}
/* Divide two numeric variables and returns the result to the third numeric variable. */
r = PGTYPESnumeric_div(numarr[i], numarr[j], d);
if (r)
{
check_errno();
printf("r: %d\n", r);
}
else
{
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type d. */
text = PGTYPESnumeric_to_asc(d, 10);
printf("num[d,%d,%d]: %s\n", i, j, text);
free(text);
}
/* Release the memory allocated to the numeric variable. */
PGTYPESnumeric_free(a);
PGTYPESnumeric_free(s);
PGTYPESnumeric_free(m);
PGTYPESnumeric_free(d);
}
}
for (i = 0; i < count; i++)
{
/* Return a pointer to a string allocated by malloc that contains the string representation of the numeric type numarr[i]. */
text = PGTYPESnumeric_to_asc(numarr[i], -1);
printf("%d: %s\n", i, text);
free(text);
/* Free memory. */
PGTYPESnumeric_free(numarr[i]);
}
free(numarr);
return (0);
}
/* Error handling */
static void
check_errno(void)
{
switch(errno)
{
case 0:
printf("(no errno set) - ");
break;
case PGTYPES_NUM_OVERFLOW:
printf("(errno == PGTYPES_NUM_OVERFLOW) - ");
break;
case PGTYPES_NUM_UNDERFLOW:
printf("(errno == PGTYPES_NUM_UNDERFLOW) - ");
break;
case PGTYPES_NUM_BAD_NUMERIC:
printf("(errno == PGTYPES_NUM_BAD_NUMERIC) - ");
break;
case PGTYPES_NUM_DIVIDE_ZERO:
printf("(errno == PGTYPES_NUM_DIVIDE_ZERO) - ");
break;
default:
printf("(unknown errno (%d))\n", errno);
printf("(libc: (%s)) ", strerror(errno));
break;
}
}
Parent topic: ECPG-based Development
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