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31.8. pgtypes library

The pgtypes library maps PostgreSQL database types to C equivalents that can be used in C programs. It also offers functions to do basic calculations with those types within C, i.e. without the help of the PostgreSQL server. See the following example:

EXEC SQL BEGIN DECLARE SECTION;
   date date1;
   timestamp ts1, tsout;
   interval iv1;
   char *out;
EXEC SQL END DECLARE SECTION;

PGTYPESdate_today(&date1);
EXEC SQL SELECT started, duration INTO :ts1, :iv1 FROM datetbl WHERE d=:date1;
PGTYPEStimestamp_add_interval(&ts1, &iv1, &tsout);
out = PGTYPEStimestamp_to_asc(&tsout);
printf("Started + duration: %s\n", out);
free(out);

31.8.1. The numeric type

The numeric type offers to do calculations with arbitrary precision. See Section 8.1 for the equivalent type in the PostgreSQL server. Because of the arbitrary precision this variable needs to be able to expand and shrink dynamically. That's why you can only create variables on the heap by means of the PGTYPESnumeric_new and PGTYPESnumeric_free functions. The decimal type, which is similar but limited in the precision, can be created on the stack as well as on the heap.

The following functions can be used to work with the numeric type:

PGTYPESnumeric_new

Request a pointer to a newly allocated numeric variable.

numeric *PGTYPESnumeric_new(void);
PGTYPESnumeric_free

Free a numeric type, release all of its memory.

void PGTYPESnumeric_free(numeric *var);
PGTYPESnumeric_from_asc

Parse a numeric type from its string notation.

numeric *PGTYPESnumeric_from_asc(char *str, char **endptr);

Valid formats are for example: -2, .794, +3.44, 592.49E07 or -32.84e-4. If the value could be parsed successfully, a valid pointer is returned, else the NULL pointer. At the moment ecpg always parses the complete string and so it currently does not support to store the address of the first invalid character in *endptr. You can safely set endptr to NULL.

PGTYPESnumeric_to_asc

Returns a pointer to a string allocated by malloc that contains the string representation of the numeric type num.

char *PGTYPESnumeric_to_asc(numeric *num, int dscale);

The numeric value will be printed with dscale decimal digits, with rounding applied if necessary.

PGTYPESnumeric_add

Add two numeric variables into a third one.

int PGTYPESnumeric_add(numeric *var1, numeric *var2, numeric *result);

The function adds the variables var1 and var2 into the result variable result. The function returns 0 on success and -1 in case of error.

PGTYPESnumeric_sub

Subtract two numeric variables and return the result in a third one.

int PGTYPESnumeric_sub(numeric *var1, numeric *var2, numeric *result);

The function subtracts the variable var2 from the variable var1. The result of the operation is stored in the variable result. The function returns 0 on success and -1 in case of error.

PGTYPESnumeric_mul

Multiply two numeric variables and return the result in a third one.

int PGTYPESnumeric_mul(numeric *var1, numeric *var2, numeric *result);

The function multiplies the variables var1 and var2. The result of the operation is stored in the variable result. The function returns 0 on success and -1 in case of error.

PGTYPESnumeric_div

Divide two numeric variables and return the result in a third one.

int PGTYPESnumeric_div(numeric *var1, numeric *var2, numeric *result);

The function divides the variables var1 by var2. The result of the operation is stored in the variable result. The function returns 0 on success and -1 in case of error.

PGTYPESnumeric_cmp

Compare two numeric variables.

int PGTYPESnumeric_cmp(numeric *var1, numeric *var2)

This function compares two numeric variables. In case of error, INT_MAX is returned. On success, the function returns one of three possible results:

  • 1, if var1 is bigger than var2

  • -1, if var1 is smaller than var2

  • 0, if var1 and var2 are equal

PGTYPESnumeric_from_int

Convert an int variable to a numeric variable.

int PGTYPESnumeric_from_int(signed int int_val, numeric *var);

This function accepts a variable of type signed int and stores it in the numeric variable var. Upon success, 0 is returned and -1 in case of a failure.

PGTYPESnumeric_from_long

Convert a long int variable to a numeric variable.

int PGTYPESnumeric_from_long(signed long int long_val, numeric *var);

This function accepts a variable of type signed long int and stores it in the numeric variable var. Upon success, 0 is returned and -1 in case of a failure.

PGTYPESnumeric_copy

Copy over one numeric variable into another one.

int PGTYPESnumeric_copy(numeric *src, numeric *dst);

This function copies over the value of the variable that src points to into the variable that dst points to. It returns 0 on success and -1 if an error occurs.

PGTYPESnumeric_from_double

Convert a variable of type double to a numeric.

int  PGTYPESnumeric_from_double(double d, numeric *dst);

This function accepts a variable of type double and stores the result in the variable that dst points to. It returns 0 on success and -1 if an error occurs.

PGTYPESnumeric_to_double

Convert a variable of type numeric to double.

int PGTYPESnumeric_to_double(numeric *nv, double *dp)

The function converts the numeric value from the variable that nv points to into the double variable that dp points to. It returns 0 on success and -1 if an error occurs, including overflow. On overflow, the global variable errno will be set to PGTYPES_NUM_OVERFLOW additionally.

PGTYPESnumeric_to_int

Convert a variable of type numeric to int.

int PGTYPESnumeric_to_int(numeric *nv, int *ip);

The function converts the numeric value from the variable that nv points to into the integer variable that ip points to. It returns 0 on success and -1 if an error occurs, including overflow. On overflow, the global variable errno will be set to PGTYPES_NUM_OVERFLOW additionally.

PGTYPESnumeric_to_long

Convert a variable of type numeric to long.

int PGTYPESnumeric_to_long(numeric *nv, long *lp);

The function converts the numeric value from the variable that nv points to into the long integer variable that lp points to. It returns 0 on success and -1 if an error occurs, including overflow. On overflow, the global variable errno will be set to PGTYPES_NUM_OVERFLOW additionally.

PGTYPESnumeric_to_decimal

Convert a variable of type numeric to decimal.

int PGTYPESnumeric_to_decimal(numeric *src, decimal *dst);

The function converts the numeric value from the variable that src points to into the decimal variable that dst points to. It returns 0 on success and -1 if an error occurs, including overflow. On overflow, the global variable errno will be set to PGTYPES_NUM_OVERFLOW additionally.

PGTYPESnumeric_from_decimal

Convert a variable of type decimal to numeric.

int PGTYPESnumeric_from_decimal(decimal *src, numeric *dst);

The function converts the decimal value from the variable that src points to into the numeric variable that dst points to. It returns 0 on success and -1 if an error occurs. Since the decimal type is implemented as a limited version of the numeric type, overflow can not occur with this conversion.

31.8.2. The date type

The date type in C enables your programs to deal with data of the SQL type date. See Section 8.5 for the equivalent type in the PostgreSQL server.

The following functions can be used to work with the date type:

PGTYPESdate_from_timestamp

Extract the date part from a timestamp.

date PGTYPESdate_from_timestamp(timestamp dt);

The function receives a timestamp as its only argument and returns the extracted date part from this timestamp.

PGTYPESdate_from_asc

Parse a date from its textual representation.

date PGTYPESdate_from_asc(char *str, char **endptr);

The function receives a C char* string str and a pointer to a C char* string endptr. At the moment ecpg always parses the complete string and so it currently does not support to store the address of the first invalid character in *endptr. You can safely set endptr to NULL.

Note that the function always assumes MDY-formatted dates and there is currently no variable to change that within ecpg.

The following input formats are allowed:

Table 31-1. Valid input formats for PGTYPESdate_from_asc

Input Result
January 8, 1999 January 8, 1999
1999-01-08 January 8, 1999
1/8/1999 January 8, 1999
1/18/1999 January 18, 1999
01/02/03 February 1, 2003
1999-Jan-08 January 8, 1999
Jan-08-1999 January 8, 1999
08-Jan-1999 January 8, 1999
99-Jan-08 January 8, 1999
08-Jan-99 January 8, 1999
08-Jan-06 January 8, 2006
Jan-08-99 January 8, 1999
19990108 ISO 8601; January 8, 1999
990108 ISO 8601; January 8, 1999
1999.008 year and day of year
J2451187 Julian day
January 8, 99 BC year 99 before the Common Era
PGTYPESdate_to_asc

Return the textual representation of a date variable.

char *PGTYPESdate_to_asc(date dDate);

The function receives the date dDate as its only parameter. It will output the date in the form 1999-01-18, i.e. in the YYYY-MM-DD format.

PGTYPESdate_julmdy

Extract the values for the day, the month and the year from a variable of type date.

void PGTYPESdate_julmdy(date d, int *mdy);

The function receives the date d and a pointer to an array of 3 integer values mdy. The variable name indicates the sequential order: mdy[0] will be set to contain the number of the month, mdy[1] will be set to the value of the day and mdy[2] will contain the year.

PGTYPESdate_mdyjul

Create a date value from an array of 3 integers that specify the day, the month and the year of the date.

void PGTYPESdate_mdyjul(int *mdy, date *jdate);

The function receives the array of the 3 integers (mdy) as its first argument and as its second argument a pointer to a variable of type date that should hold the result of the operation.

PGTYPESdate_dayofweek

Return a number representing the day of the week for a date value.

int PGTYPESdate_dayofweek(date d);

The function receives the date variable d as its only argument and returns an integer that indicates the day of the week for this date.

  • 0 - Sunday

  • 1 - Monday

  • 2 - Tuesday

  • 3 - Wednesday

  • 4 - Thursday

  • 5 - Friday

  • 6 - Saturday

PGTYPESdate_today

Get the current date.

void PGTYPESdate_today(date *d);

The function receives a pointer to a date variable (d) that it sets to the current date.

PGTYPESdate_fmt_asc

Convert a variable of type date to its textual representation using a format mask.

int PGTYPESdate_fmt_asc(date dDate, char *fmtstring, char *outbuf);

The function receives the date to convert (dDate), the format mask (fmtstring) and the string that will hold the textual representation of the date (outbuf).

On success, 0 is returned and a negative value if an error occurred.

The following literals are the field specifiers you can use:

  • dd - The number of the day of the month.

  • mm - The number of the month of the year.

  • yy - The number of the year as a two digit number.

  • yyyy - The number of the year as a four digit number.

  • ddd - The name of the day (abbreviated).

  • mmm - The name of the month (abbreviated).

All other characters are copied 1:1 to the output string.

The following table indicates a few possible formats. This will give you an idea of how to use this function. All output lines are based on the same date: November, 23rd, 1959.

Table 31-2. Valid input formats for PGTYPESdate_fmt_asc

fmt result
mmddyy 112359
ddmmyy 231159
yymmdd 591123
yy/mm/dd 59/11/23
yy mm dd 59 11 23
yy.mm.dd 59.11.23
.mm.yyyy.dd. .11.1959.23.
mmm. dd, yyyy Nov. 23, 1959
mmm dd yyyy Nov 23 1959
yyyy dd mm 1959 23 11
ddd, mmm. dd, yyyy Mon, Nov. 23, 1959
(ddd) mmm. dd, yyyy (Mon) Nov. 23, 1959
PGTYPESdate_defmt_asc

Use a format mask to convert a C char* string to a value of type date.

int PGTYPESdate_defmt_asc(date *d, char *fmt, char *str);

The function receives a pointer to the date value that should hold the result of the operation (d), the format mask to use for parsing the date (fmt) and the C char* string containing the textual representation of the date (str). The textual representation is expected to match the format mask. However you do not need to have a 1:1 mapping of the string to the format mask. The function only analyzes the sequential order and looks for the literals yy or yyyy that indicate the position of the year, mm to indicate the position of the month and dd to indicate the position of the day.

The following table indicates a few possible formats. This will give you an idea of how to use this function.

Table 31-3. Valid input formats for rdefmtdate

fmt str result
ddmmyy 21-2-54 1954-02-21
ddmmyy 2-12-54 1954-12-02
ddmmyy 20111954 1954-11-20
ddmmyy 130464 1964-04-13
mmm.dd.yyyy MAR-12-1967 1967-03-12
yy/mm/dd 1954, February 3rd 1954-02-03
mmm.dd.yyyy 041269 1969-04-12
yy/mm/dd In the year 2525, in the month of July, mankind will be alive on the 28th day 2525-07-28
dd-mm-yy I said on the 28th of July in the year 2525 2525-07-28
mmm.dd.yyyy 9/14/58 1958-09-14
yy/mm/dd 47/03/29 1947-03-29
mmm.dd.yyyy oct 28 1975 1975-10-28
mmddyy Nov 14th, 1985 1985-11-14

31.8.3. The timestamp type

The timestamp type in C enables your programs to deal with data of the SQL type timestamp. See Section 8.5 for the equivalent type in the PostgreSQL server.

The following functions can be used to work with the timestamp type:

PGTYPEStimestamp_from_asc

Parse a timestamp from its textual representation into a timestamp variable.

timestamp PGTYPEStimestamp_from_asc(char *str, char **endptr);

The function receives the string to parse (str) and a pointer to a C char* (endptr). At the moment ecpg always parses the complete string and so it currently does not support to store the address of the first invalid character in *endptr. You can safely set endptr to NULL.

The function returns the parsed timestamp on success. On error, PGTYPESInvalidTimestamp is returned and errno is set to PGTYPES_TS_BAD_TIMESTAMP. See PGTYPESInvalidTimestamp for important notes on this value.

In general, the input string can contain any combination of an allowed date specification, a whitespace character and an allowed time specification. Note that timezones are not supported by ecpg. It can parse them but does not apply any calculation as the PostgreSQL server does for example. Timezone specifiers are silently discarded.

The following table contains a few examples for input strings:

Table 31-4. Valid input formats for PGTYPEStimestamp_from_asc

Input Result
1999-01-08 04:05:06 1999-01-08 04:05:06
January 8 04:05:06 1999 PST 1999-01-08 04:05:06
1999-Jan-08 04:05:06.789-8 1999-01-08 04:05:06.789 (time zone specifier ignored)
J2451187 04:05-08:00 1999-01-08 04:05:00 (time zone specifier ignored)
PGTYPEStimestamp_to_asc

Converts a date to a C char* string.

char *PGTYPEStimestamp_to_asc(timestamp tstamp);

The function receives the timestamp tstamp as its only argument and returns an allocated string that contains the textual representation of the timestamp.

PGTYPEStimestamp_current

Retrieve the current timestamp.

void PGTYPEStimestamp_current(timestamp *ts);

The function retrieves the current timestamp and saves it into the timestamp variable that ts points to.

PGTYPEStimestamp_fmt_asc

Convert a timestamp variable to a C char* using a format mask.

int PGTYPEStimestamp_fmt_asc(timestamp *ts, char *output, int str_len, char *fmtstr);

The function receives a pointer to the timestamp to convert as its first argument (ts), a pointer to the output buffer (output), the maximal length that has been allocated for the output buffer (str_len) and the format mask to use for the conversion (fmtstr).

Upon success, the function returns 0 and a negative value if an error occurred.

You can use the following format specifiers for the format mask. The format specifiers are the same ones that are used in the strftime function in libc. Any non-format specifier will be copied into the output buffer.

  • %A - is replaced by national representation of the full weekday name.

  • %a - is replaced by national representation of the abbreviated weekday name.

  • %B - is replaced by national representation of the full month name.

  • %b - is replaced by national representation of the abbreviated month name.

  • %C - is replaced by (year / 100) as decimal number; single digits are preceded by a zero.

  • %c - is replaced by national representation of time and date.

  • %D - is equivalent to %m/%d/%y.

  • %d - is replaced by the day of the month as a decimal number (01-31).

  • %E* %O* - POSIX locale extensions. The sequences %Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH %OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy are supposed to provide alternate representations.

    Additionally %OB implemented to represent alternative months names (used standalone, without day mentioned).

  • %e - is replaced by the day of month as a decimal number (1-31); single digits are preceded by a blank.

  • %F - is equivalent to %Y-%m-%d.

  • %G - is replaced by a year as a decimal number with century. This year is the one that contains the greater part of the week (Monday as the first day of the week).

  • %g - is replaced by the same year as in %G, but as a decimal number without century (00-99).

  • %H - is replaced by the hour (24-hour clock) as a decimal number (00-23).

  • %h - the same as %b.

  • %I - is replaced by the hour (12-hour clock) as a decimal number (01-12).

  • %j - is replaced by the day of the year as a decimal number (001-366).

  • %k - is replaced by the hour (24-hour clock) as a decimal number (0-23); single digits are preceded by a blank.

  • %l - is replaced by the hour (12-hour clock) as a decimal number (1-12); single digits are preceded by a blank.

  • %M - is replaced by the minute as a decimal number (00-59).

  • %m - is replaced by the month as a decimal number (01-12).

  • %n - is replaced by a newline.

  • %O* - the same as %E*.

  • %p - is replaced by national representation of either "ante meridiem" or "post meridiem" as appropriate.

  • %R - is equivalent to %H:%M.

  • %r - is equivalent to %I:%M:%S %p.

  • %S - is replaced by the second as a decimal number (00-60).

  • %s - is replaced by the number of seconds since the Epoch, UTC.

  • %T - is equivalent to %H:%M:%S

  • %t - is replaced by a tab.

  • %U - is replaced by the week number of the year (Sunday as the first day of the week) as a decimal number (00-53).

  • %u - is replaced by the weekday (Monday as the first day of the week) as a decimal number (1-7).

  • %V - is replaced by the week number of the year (Monday as the first day of the week) as a decimal number (01-53). If the week containing January 1 has four or more days in the new year, then it is week 1; otherwise it is the last week of the previous year, and the next week is week 1.

  • %v - is equivalent to %e-%b-%Y.

  • %W - is replaced by the week number of the year (Monday as the first day of the week) as a decimal number (00-53).

  • %w - is replaced by the weekday (Sunday as the first day of the week) as a decimal number (0-6).

  • %X - is replaced by national representation of the time.

  • %x - is replaced by national representation of the date.

  • %Y - is replaced by the year with century as a decimal number.

  • %y - is replaced by the year without century as a decimal number (00-99).

  • %Z - is replaced by the time zone name.

  • %z - is replaced by the time zone offset from UTC; a leading plus sign stands for east of UTC, a minus sign for west of UTC, hours and minutes follow with two digits each and no delimiter between them (common form for RFC 822 date headers).

  • %+ - is replaced by national representation of the date and time.

  • %-* - GNU libc extension. Do not do any padding when performing numerical outputs.

  • $_* - GNU libc extension. Explicitly specify space for padding.

  • %0* - GNU libc extension. Explicitly specify zero for padding.

  • %% - is replaced by %.

PGTYPEStimestamp_sub

Subtract one timestamp from another one and save the result in a variable of type interval.

int PGTYPEStimestamp_sub(timestamp *ts1, timestamp *ts2, interval *iv);

The function will subtract the timestamp variable that ts2 points to from the timestamp variable that ts1 points to and will store the result in the interval variable that iv points to.

Upon success, the function returns 0 and a negative value if an error occurred.

PGTYPEStimestamp_defmt_asc

Parse a timestamp value from its textual representation using a formatting mask.

int PGTYPEStimestamp_defmt_asc(char *str, char *fmt, timestamp *d);

The function receives the textual representation of a timestamp in the variable str as well as the formatting mask to use in the variable fmt. The result will be stored in the variable that d points to.

If the formatting mask fmt is NULL, the function will fall back to the default formatting mask which is %Y-%m-%d %H:%M:%S.

This is the reverse function to PGTYPEStimestamp_fmt_asc. See the documentation there in order to find out about the possible formatting mask entries.

PGTYPEStimestamp_add_interval

Add an interval variable to a timestamp variable.

int PGTYPEStimestamp_add_interval(timestamp *tin, interval *span, timestamp *tout);

The function receives a pointer to a timestamp variable tin and a pointer to an interval variable span. It adds the interval to the timestamp and saves the resulting timestamp in the variable that tout points to.

Upon success, the function returns 0 and a negative value if an error occurred.

PGTYPEStimestamp_sub_interval

Subtract an interval variable from a timestamp variable.

int PGTYPEStimestamp_sub_interval(timestamp *tin, interval *span, timestamp *tout);

The function subtracts the interval variable that span points to from the timestamp variable that tin points to and saves the result into the variable that tout points to.

Upon success, the function returns 0 and a negative value if an error occurred.

31.8.4. The interval type

The interval type in C enables your programs to deal with data of the SQL type interval. See Section 8.5 for the equivalent type in the PostgreSQL server.

The following functions can be used to work with the interval type:

PGTYPESinterval_new

Return a pointer to a newly allocated interval variable.

interval *PGTYPESinterval_new(void);
PGTYPESinterval_free

Release the memory of a previously allocated interval variable.

void PGTYPESinterval_new(interval *intvl);
PGTYPESinterval_from_asc

Parse an interval from its textual representation.

interval *PGTYPESinterval_from_asc(char *str, char **endptr);

The function parses the input string str and returns a pointer to an allocated interval variable. At the moment ecpg always parses the complete string and so it currently does not support to store the address of the first invalid character in *endptr. You can safely set endptr to NULL.

PGTYPESinterval_to_asc

Convert a variable of type interval to its textual representation.

char *PGTYPESinterval_to_asc(interval *span);

The function converts the interval variable that span points to into a C char*. The output looks like this example: @ 1 day 12 hours 59 mins 10 secs.

PGTYPESinterval_copy

Copy a variable of type interval.

int PGTYPESinterval_copy(interval *intvlsrc, interval *intvldest);

The function copies the interval variable that intvlsrc points to into the variable that intvldest points to. Note that you need to allocate the memory for the destination variable before.

31.8.5. The decimal type

The decimal type is similar to the numeric type. However it is limited to a maximal precision of 30 significant digits. In contrast to the numeric type which can be created on the heap only, the decimal type can be created either on the stack or on the heap (by means of the functions PGTYPESdecimal_new() and PGTYPESdecimal_free(). There are a lot of other functions that deal with the decimal type in the Informix compatibility mode described in Section 31.9.

The following functions can be used to work with the decimal type and are not only contained in the libcompat library.

PGTYPESdecimal_new

Request a pointer to a newly allocated decimal variable.

decimal *PGTYPESdecimal_new(void);
PGTYPESdecimal_free

Free a decimal type, release all of its memory.

void PGTYPESdecimal_free(decimal *var);

31.8.6. errno values of pgtypeslib

PGTYPES_NUM_BAD_NUMERIC

An argument should contain a numeric variable (or point to a numeric variable) but in fact its in-memory representation was invalid.

PGTYPES_NUM_OVERFLOW

An overflow occurred. Since the numeric type can deal with almost arbitrary precision, converting a numeric variable into other types might cause overflow.

PGTYPES_NUM_OVERFLOW

An underflow occurred. Since the numeric type can deal with almost arbitrary precision, converting a numeric variable into other types might cause underflow.

PGTYPES_NUM_DIVIDE_ZERO

A division by zero has been attempted.

PGTYPES_DATE_BAD_DATE
PGTYPES_DATE_ERR_EARGS
PGTYPES_DATE_ERR_ENOSHORTDATE
PGTYPES_INTVL_BAD_INTERVAL
PGTYPES_DATE_ERR_ENOTDMY
PGTYPES_DATE_BAD_DAY
PGTYPES_DATE_BAD_MONTH
PGTYPES_TS_BAD_TIMESTAMP

31.8.7. Special constants of pgtypeslib

PGTYPESInvalidTimestamp

A value of type timestamp representing an invalid time stamp. This is returned by the function PGTYPEStimestamp_from_asc on parse error. Note that due to the internal representation of the timestamp datatype, PGTYPESInvalidTimestamp is also a valid timestamp at the same time. It is set to 1899-12-31 23:59:59. In order to detect errors, make sure that your application does not only test for PGTYPESInvalidTimestamp but also for errno != 0 after each call to PGTYPEStimestamp_from_asc.

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