How to map c code to postgres c function format?
I'm trying to write the following c code in postgres c function style -
The argument passed is a value of a table column of type varchar,
Needed some help to map this pure C code in the postgres C format of the type -
Datum
func_name (PG_FUNCTION_ARGS)
Can somebody please help to map this and return the appropriate char value?
static uint32_t key = 0xOQ9426YP;
uint32_t tmpKey = 0x00000000;
int i = 0;
uint32_t *in = (uint32_t *) str;
uint32_t *out = (uint32_t *) malloc (256);
memset (out, 0, 256);
tmpKey = key;
for (i = 0; i < (256/sizeof (uint32_t)); i++)
{
out[i] = tmpKey ^ in[i];
tmpKey = out[i];
}
memcpy (output, (char *) out, 256);
Thanks & Regards,
VJ
c postgresql
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
add a comment |
I'm trying to write the following c code in postgres c function style -
The argument passed is a value of a table column of type varchar,
Needed some help to map this pure C code in the postgres C format of the type -
Datum
func_name (PG_FUNCTION_ARGS)
Can somebody please help to map this and return the appropriate char value?
static uint32_t key = 0xOQ9426YP;
uint32_t tmpKey = 0x00000000;
int i = 0;
uint32_t *in = (uint32_t *) str;
uint32_t *out = (uint32_t *) malloc (256);
memset (out, 0, 256);
tmpKey = key;
for (i = 0; i < (256/sizeof (uint32_t)); i++)
{
out[i] = tmpKey ^ in[i];
tmpKey = out[i];
}
memcpy (output, (char *) out, 256);
Thanks & Regards,
VJ
c postgresql
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
This code completely ignores endianness. Is that your intention?
– paddy
Nov 22 '18 at 4:24
On top of that,0xOQ9426YPis not a valid hexadecimal literal.
– paddy
Nov 22 '18 at 4:27
add a comment |
I'm trying to write the following c code in postgres c function style -
The argument passed is a value of a table column of type varchar,
Needed some help to map this pure C code in the postgres C format of the type -
Datum
func_name (PG_FUNCTION_ARGS)
Can somebody please help to map this and return the appropriate char value?
static uint32_t key = 0xOQ9426YP;
uint32_t tmpKey = 0x00000000;
int i = 0;
uint32_t *in = (uint32_t *) str;
uint32_t *out = (uint32_t *) malloc (256);
memset (out, 0, 256);
tmpKey = key;
for (i = 0; i < (256/sizeof (uint32_t)); i++)
{
out[i] = tmpKey ^ in[i];
tmpKey = out[i];
}
memcpy (output, (char *) out, 256);
Thanks & Regards,
VJ
c postgresql
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
I'm trying to write the following c code in postgres c function style -
The argument passed is a value of a table column of type varchar,
Needed some help to map this pure C code in the postgres C format of the type -
Datum
func_name (PG_FUNCTION_ARGS)
Can somebody please help to map this and return the appropriate char value?
static uint32_t key = 0xOQ9426YP;
uint32_t tmpKey = 0x00000000;
int i = 0;
uint32_t *in = (uint32_t *) str;
uint32_t *out = (uint32_t *) malloc (256);
memset (out, 0, 256);
tmpKey = key;
for (i = 0; i < (256/sizeof (uint32_t)); i++)
{
out[i] = tmpKey ^ in[i];
tmpKey = out[i];
}
memcpy (output, (char *) out, 256);
Thanks & Regards,
VJ
c postgresql
c postgresql
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
asked Nov 22 '18 at 3:59
Being VJBeing VJ
41
41
This code completely ignores endianness. Is that your intention?
– paddy
Nov 22 '18 at 4:24
On top of that,0xOQ9426YPis not a valid hexadecimal literal.
– paddy
Nov 22 '18 at 4:27
add a comment |
This code completely ignores endianness. Is that your intention?
– paddy
Nov 22 '18 at 4:24
On top of that,0xOQ9426YPis not a valid hexadecimal literal.
– paddy
Nov 22 '18 at 4:27
This code completely ignores endianness. Is that your intention?
– paddy
Nov 22 '18 at 4:24
This code completely ignores endianness. Is that your intention?
– paddy
Nov 22 '18 at 4:24
On top of that,
0xOQ9426YP is not a valid hexadecimal literal.– paddy
Nov 22 '18 at 4:27
On top of that,
0xOQ9426YP is not a valid hexadecimal literal.– paddy
Nov 22 '18 at 4:27
add a comment |
1 Answer
1
active
oldest
votes
For data PostgreSQL uses own internal format and structures that should not be compatible with C language. For strings a varlena format is used - in this format first N bytes are encoded length - and after these bytes are encoded data. The direct access is not recommended - for almost all work there are a macros.
For example - some small function hello can looks like:
Datum
Hello(PG_FUNCTION_ARGS)
{
text *txt = PG_GETARG_TEXT_PP(0);
text *result;
char *str;
char *hello = "Hello, ";
int size;
int hello_size;
-- conversion to c string
str = text_to_cstring(txt);
-- show it on debug console
elog(NOTICE, "input string: %s", str);
hello_size = strlen(hello);
size = hello_size + VARSIZE_ANY_EXHDR(txt) + VARHDRSZ;
-- allocate memory for result, use palloc, not malloc!
result = palloc(size);
--set size of result varlena type
SET_VARSIZE(result, size);
-- set data
memcpy(VARDATA(result), str, hello_size);
memcpy(VARDATA(result) + hello_size,
VARDATA_ANY(txt), VARSIZE_ANY_EXHDR(txt));
-- returns data
PG_RETURN_TEXT_P(result);
}
You can see, this is C and it is not C. There are lot of macros, than can be used a) for portability purposes, b) for hiding complexity. It is good to start to read documentation or some presentation.
This topic is not too hard or too complex, but it is not intuitive - you cannot to start without reading documentation.
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
For data PostgreSQL uses own internal format and structures that should not be compatible with C language. For strings a varlena format is used - in this format first N bytes are encoded length - and after these bytes are encoded data. The direct access is not recommended - for almost all work there are a macros.
For example - some small function hello can looks like:
Datum
Hello(PG_FUNCTION_ARGS)
{
text *txt = PG_GETARG_TEXT_PP(0);
text *result;
char *str;
char *hello = "Hello, ";
int size;
int hello_size;
-- conversion to c string
str = text_to_cstring(txt);
-- show it on debug console
elog(NOTICE, "input string: %s", str);
hello_size = strlen(hello);
size = hello_size + VARSIZE_ANY_EXHDR(txt) + VARHDRSZ;
-- allocate memory for result, use palloc, not malloc!
result = palloc(size);
--set size of result varlena type
SET_VARSIZE(result, size);
-- set data
memcpy(VARDATA(result), str, hello_size);
memcpy(VARDATA(result) + hello_size,
VARDATA_ANY(txt), VARSIZE_ANY_EXHDR(txt));
-- returns data
PG_RETURN_TEXT_P(result);
}
You can see, this is C and it is not C. There are lot of macros, than can be used a) for portability purposes, b) for hiding complexity. It is good to start to read documentation or some presentation.
This topic is not too hard or too complex, but it is not intuitive - you cannot to start without reading documentation.
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
add a comment |
For data PostgreSQL uses own internal format and structures that should not be compatible with C language. For strings a varlena format is used - in this format first N bytes are encoded length - and after these bytes are encoded data. The direct access is not recommended - for almost all work there are a macros.
For example - some small function hello can looks like:
Datum
Hello(PG_FUNCTION_ARGS)
{
text *txt = PG_GETARG_TEXT_PP(0);
text *result;
char *str;
char *hello = "Hello, ";
int size;
int hello_size;
-- conversion to c string
str = text_to_cstring(txt);
-- show it on debug console
elog(NOTICE, "input string: %s", str);
hello_size = strlen(hello);
size = hello_size + VARSIZE_ANY_EXHDR(txt) + VARHDRSZ;
-- allocate memory for result, use palloc, not malloc!
result = palloc(size);
--set size of result varlena type
SET_VARSIZE(result, size);
-- set data
memcpy(VARDATA(result), str, hello_size);
memcpy(VARDATA(result) + hello_size,
VARDATA_ANY(txt), VARSIZE_ANY_EXHDR(txt));
-- returns data
PG_RETURN_TEXT_P(result);
}
You can see, this is C and it is not C. There are lot of macros, than can be used a) for portability purposes, b) for hiding complexity. It is good to start to read documentation or some presentation.
This topic is not too hard or too complex, but it is not intuitive - you cannot to start without reading documentation.
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
add a comment |
For data PostgreSQL uses own internal format and structures that should not be compatible with C language. For strings a varlena format is used - in this format first N bytes are encoded length - and after these bytes are encoded data. The direct access is not recommended - for almost all work there are a macros.
For example - some small function hello can looks like:
Datum
Hello(PG_FUNCTION_ARGS)
{
text *txt = PG_GETARG_TEXT_PP(0);
text *result;
char *str;
char *hello = "Hello, ";
int size;
int hello_size;
-- conversion to c string
str = text_to_cstring(txt);
-- show it on debug console
elog(NOTICE, "input string: %s", str);
hello_size = strlen(hello);
size = hello_size + VARSIZE_ANY_EXHDR(txt) + VARHDRSZ;
-- allocate memory for result, use palloc, not malloc!
result = palloc(size);
--set size of result varlena type
SET_VARSIZE(result, size);
-- set data
memcpy(VARDATA(result), str, hello_size);
memcpy(VARDATA(result) + hello_size,
VARDATA_ANY(txt), VARSIZE_ANY_EXHDR(txt));
-- returns data
PG_RETURN_TEXT_P(result);
}
You can see, this is C and it is not C. There are lot of macros, than can be used a) for portability purposes, b) for hiding complexity. It is good to start to read documentation or some presentation.
This topic is not too hard or too complex, but it is not intuitive - you cannot to start without reading documentation.
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
For data PostgreSQL uses own internal format and structures that should not be compatible with C language. For strings a varlena format is used - in this format first N bytes are encoded length - and after these bytes are encoded data. The direct access is not recommended - for almost all work there are a macros.
For example - some small function hello can looks like:
Datum
Hello(PG_FUNCTION_ARGS)
{
text *txt = PG_GETARG_TEXT_PP(0);
text *result;
char *str;
char *hello = "Hello, ";
int size;
int hello_size;
-- conversion to c string
str = text_to_cstring(txt);
-- show it on debug console
elog(NOTICE, "input string: %s", str);
hello_size = strlen(hello);
size = hello_size + VARSIZE_ANY_EXHDR(txt) + VARHDRSZ;
-- allocate memory for result, use palloc, not malloc!
result = palloc(size);
--set size of result varlena type
SET_VARSIZE(result, size);
-- set data
memcpy(VARDATA(result), str, hello_size);
memcpy(VARDATA(result) + hello_size,
VARDATA_ANY(txt), VARSIZE_ANY_EXHDR(txt));
-- returns data
PG_RETURN_TEXT_P(result);
}
You can see, this is C and it is not C. There are lot of macros, than can be used a) for portability purposes, b) for hiding complexity. It is good to start to read documentation or some presentation.
This topic is not too hard or too complex, but it is not intuitive - you cannot to start without reading documentation.
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
answered Nov 22 '18 at 4:57
Pavel StehulePavel Stehule
22.6k34857
22.6k34857
add a comment |
add a comment |
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This code completely ignores endianness. Is that your intention?
– paddy
Nov 22 '18 at 4:24
On top of that,
0xOQ9426YPis not a valid hexadecimal literal.– paddy
Nov 22 '18 at 4:27