Using Curl for inverse geocoding _c language to write dynamic link libraries to extend PostgreSQL

Process:
"1" C language to write inverse geocoding functions, using Curl Library and the German server for geographical coordinates resolution
"2" GCC build dynamic link library
Functions in "3" PostgreSQL loaded in a dynamic-link library
Conversion of Inverse geocoding function return type in "4" PostgreSQL
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"1" C language to write inverse geocoding functions, using Curl Library and the German server for geographical coordinates resolution

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl / curl.h>

#include "postgres.h"
#include "fmgr.h"

PG_MODULE_MAGIC;

int StringFind (const char * pSrc, const char * pDst) // String position search, returns the position of the source string
{
    int i, j;
    for (i = 0; pSrc [i]! = '\ 0'; i ++)
    {
        if (pSrc [i]! = pDst [0])
            continue;
        j = 0;
        while (pDst [j]! = '\ 0' && pSrc [i + j]! = '\ 0')
        {
            j ++;
            if (pDst [j]! = pSrc [i + j])
            break;
        }
        if (pDst [j] == '\ 0')
            return i;
    }
    return -1;
}

size_t write_callback (char * ptr, size_t size, size_t nmemb, void * userdata) // callback function
{
strcat ((char *) userdata, (char *) ptr);
return size * nmemb;
}

char * poi_list (char * longitude, char * latitude) {// Main function

int mPos = 0;
char * result;
char * strLongitude = longitude;
char * strLatitude = latitude;

char tempLongitude [25] = "longitude =";
char tempLatitude [25] = "& latitude =";
char * pstrLongitude;
char * pstrLatitude;
Ranch
pstrLongitude = strcat ((char *) tempLongitude, strLongitude);
pstrLatitude = strcat ((char *) tempLatitude, strLatitude);
char * locationInfor = strcat (pstrLongitude, pstrLatitude);

char finalResult [5120] = {'\ 0'};
int i = 0;
char * pDst = "poi_list";
 char szRet [5120] = {'\ 0'}; // result storage
char szpage [256] = "http://ditu.amap.com/service/regeo?";
char * myurl = strcat (szpage, locationInfor);

CURLcode res;
res = curl_global_init (CURL_GLOBAL_ALL); // Init
if (res! = CURLE_OK)
{
result = psprintf ("Failed to global init default [% d] \ n", res);
     return result;
}

CURL * pEasyHandle = curl_easy_init (); // initialize
Ranch
curl_easy_setopt (pEasyHandle, CURLOPT_URL, myurl); // Incoming URL
curl_easy_setopt (pEasyHandle, CURLOPT_WRITEFUNCTION, & write_callback); // Call the callback function
curl_easy_setopt (pEasyHandle, CURLOPT_TIMEOUT, 10);
curl_easy_setopt (pEasyHandle, CURLOPT_FORBID_REUSE, 1);
curl_easy_setopt (pEasyHandle, CURLOPT_WRITEDATA, szRet); // parameter three corresponds to parameter four of the callback

res = curl_easy_perform (pEasyHandle);
curl_easy_cleanup (pEasyHandle);

result = szRet; // Get the entire json data
Ranch
mPos = StringFind (result, pDst);
Ranch
int mNewPos = mPos + 10; // Filter out the poi_list field

while (szRet [mNewPos]! = '\ 0')
{

finalResult [i] = szRet [mNewPos];
mNewPos ++;
i ++;
}
i = i-2;
finalResult [i] = '\ 0';
char * result0 = finalResult;
return result0;
}

"2" GCC build dynamic link library

[email protected]: ~ / documents / Curl_program $ gcc -fpic -I `pg_config --includedir-server` -c poiOutput.c -lcurl
[email protected]: ~ / documents / Curl_program $ gcc -fpic -shared -o poiOutput.so poiOutput.o -lcurl
[email protected]: ~ / documents / Curl_program $ sudo cp poiOutput.so `pg_config --libdir`

functions in "3" PostgreSQL loaded in a dynamic-link library

gpsDB=# load 'poiOutput.so';
LOAD
gpsDB=# create function poi_list(cstring,cstring)
returns cstring
as 'poiOutput.so','poi_list'
language C immutable strict;
CREATE FUNCTION
gpsDB=# select poi_list('118.744607','32.030886');

"4" PostgreSQL converts the return type of the inverse geocoding function to "parameter null::p Oiarray, where the Poiarray table structure corresponds to the JSON structure, click here for details"

gpsDB = # select (select poi_list ('112.931850', '28.169100')) :: json;
ERROR: cannot cast type cstring to json? // cstring type is converted to text type, and then converted to json type
gpsDB = # select * from json_populate_recordset (null :: poiarray, (cast ((select poi_list ('118.744607', '32.030886')) as text)) :: json);
gpsDB = # select * from json_populate_recordset (null :: poiarray, (poi_list ('118.744607', '32.030886') :: text) :: json);  

Using Curl for inverse geocoding _c language to write dynamic link libraries to extend PostgreSQL