cpostgresqllibpqbytea

Retrieving image file from Postgresql database returns two times bigger data inserted (by libpq library)

I'm using libpq library of Postgresql database and I have a problem about retrieving the bytea data from db. I couldn't solve my problem, so wanted to ask you. Whenever I try to insert an image file into db and get it back, the size of returning data is always 2 times of the data I sent. Actually, the exact equation is : retrieved data = sent data * 2 + 2.(in bytes). So, I couldn't figure it out yet, I'm probably missing something :/

An example code I use is like below : 

PGresult*    res;
const char*  paramValues[1] = {plateImageArray.data()}; // data type is const char*
int          paramLengths[1] = {plateImageArray.size()}; // size of image is 58573 bytes
int          paramFormats[1] = {1}; // 1 for byte, 0 for text

res = PQexecParams(conn,
        "INSERT INTO \"plates\" (plateImage) VALUES ($1::bytea)",
        1,               /* param number */
        NULL,            /* param type */
        paramValues,     /* param values*/
        paramLengths,    /* param lengths */
        paramFormats,    /* default to all text params */
        1);              /* return type, 1 for text. */

res = PQexec(conn,"Select * from \"plate_images\" WHERE ...."); /*returns 1 tuple : something / something / image(bytea) */

int lengthOfPlateImage=PQgetlength(res,0,2); // indicates 117148 bytes, exactly 2 times of sent data +2

I appreciate if you guys help me. I'm deadly bored of searching about the reason of it.

Thanks in advance.

Edit: I tracked the data stored in disk and the size of inserted data is the same (58573 byte). Two times bigger data becomes while getting it ...

Solution

  • Okay, the query made with "PQexec" command returns the value in text format and it has no parameter to tell whether you want the result in text format or byte. I am not sure if a better and more suitable command exists to query it but I used "PQexecParams" and set the return type 1 (1 for byte, 0 for text) and it returned the exact data with the expected size. Thanks anyhow.