https://github.com/rsim/oracle-enhanced/issues/1755

lob-read-test.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <oci.h>

/*
Run the following SQL in advance.

drop table clob_test_1755 purge;
create table clob_test_1755 (clob_col clob);
insert into clob_test_1755 values (empty_clob());
commit;

*/

/* Change the following three values */
const char *username = "username";
const char *password = "password";
const char *database = "";

static void checkerr(void *handle, ub4 htype, sword status, const char *func)
{
    text errbuf[512];
    sb4 errcode = 0;

    switch (status) {
    case OCI_SUCCESS:
    case OCI_SUCCESS_WITH_INFO:
        return;
        break;
    case OCI_NEED_DATA:
        printf("    %s => OCI_NEED_DATA\n", func);
        break;
    case OCI_NO_DATA:
        printf("    %s => OCI_NO_DATA\n", func);
        break;
    case OCI_ERROR:
        OCIErrorGet(handle, 1, NULL, &errcode, errbuf, sizeof(errbuf), htype);
        printf("    %s => OCI_ERROR\n    %.*s\n", func, (int)sizeof(errbuf), errbuf);
        break;
    case OCI_INVALID_HANDLE:
        printf("    %s => OCI_INVALID_HANDLE\n", func);
        break;
    case OCI_STILL_EXECUTING:
        printf("    %s => OCI_STILL_EXECUTE\n", func);
        break;
    case OCI_CONTINUE:
        printf("    %s => OCI_CONTINUE\n", func);
        break;
    default:
        printf("    %s => Unknown %d\n", func, status);
    }
    exit(1);
}

#define chke(func) do { \
    sword status = (func); \
    if (status != OCI_SUCCESS) { \
        checkerr(envhp, OCI_HTYPE_ENV, status, #func); \
    } \
} while (0)

#define chk(func) do { \
    sword status = (func); \
    if (status != OCI_SUCCESS) { \
        checkerr(errhp, OCI_HTYPE_ERROR, status, #func); \
    } \
} while (0)

static void read_lob_using_OCILobRead2(OCISvcCtx *svchp, OCIError *errhp, OCILobLocator *lob);
static void read_lob_using_OCILobArrayRead(OCISvcCtx *svchp, OCIError *errhp, OCILobLocator *lob);

int main()
{
    OCIEnv *envhp;
    OCISvcCtx *svchp;
    OCIServer *srvhp;
    OCISession *seshp;
    OCIError *errhp;
    OCIStmt *stmtp;
    OCIDefine *defnp;
    const char *sql = "select clob_col from clob_test_1755";
    OCILobLocator *lob;

    /* allocate handles */
    chke(OCIEnvCreate(&envhp, OCI_DEFAULT, NULL, NULL, NULL, NULL, 0, NULL));
    chke(OCIHandleAlloc(envhp, (dvoid**)&svchp, OCI_HTYPE_SVCCTX, 0, NULL));
    chke(OCIHandleAlloc(envhp, (dvoid**)&srvhp, OCI_HTYPE_SERVER, 0, NULL));
    chke(OCIHandleAlloc(envhp, (dvoid**)&seshp, OCI_HTYPE_SESSION, 0, NULL));
    chke(OCIHandleAlloc(envhp, (dvoid**)&errhp, OCI_HTYPE_ERROR, 0, NULL));
    chke(OCIDescriptorAlloc(envhp, (dvoid**)&lob, OCI_DTYPE_LOB, 0, NULL));

    /* connect */
    chk(OCIServerAttach(srvhp, errhp, (const text*)database, strlen(database), OCI_DEFAULT));
    chk(OCIAttrSet(seshp, OCI_HTYPE_SESSION, (void*)username, strlen(username), OCI_ATTR_USERNAME, errhp));
    chk(OCIAttrSet(seshp, OCI_HTYPE_SESSION, (void*)password, strlen(password), OCI_ATTR_PASSWORD, errhp));
    chk(OCIAttrSet(svchp, OCI_HTYPE_SVCCTX, srvhp, 0, OCI_ATTR_SERVER, errhp));
    chk(OCIAttrSet(svchp, OCI_HTYPE_SVCCTX, seshp, 0, OCI_ATTR_SESSION, errhp));
    chk(OCISessionBegin(svchp, errhp, seshp, OCI_CRED_RDBMS, OCI_DEFAULT));

    /* prepare, execute and fetch */
    chk(OCIStmtPrepare2(svchp, &stmtp, errhp, (const text*)sql, strlen(sql), NULL, 0, OCI_NTV_SYNTAX, OCI_DEFAULT));
    chk(OCIDefineByPos(stmtp, &defnp, errhp, 1, &lob, 0, SQLT_CLOB, NULL, NULL, NULL, OCI_DEFAULT));
    chk(OCIStmtExecute(svchp, stmtp, errhp, 0, 0, NULL, NULL, OCI_DEFAULT));
    chk(OCIStmtFetch(stmtp, errhp, 1, OCI_FETCH_NEXT, OCI_DEFAULT));

    read_lob_using_OCILobRead2(svchp, errhp, lob);
    read_lob_using_OCILobArrayRead(svchp, errhp, lob);
    return 0;
}

static void read_lob_using_OCILobRead2(OCISvcCtx *svchp, OCIError *errhp, OCILobLocator *lob)
{
    oraub8 byte_amt = 0;
    oraub8 char_amt = UB4MAXVAL;
    char buf[50];

    chk(OCILobRead2(svchp, errhp, lob, &byte_amt, &char_amt, 1, buf, sizeof(buf), OCI_ONE_PIECE, NULL, NULL, 0, SQLCS_IMPLICIT));
    printf("len=%d, data='%.*s'\n", (int)byte_amt, (int)byte_amt, buf);
}

static void read_lob_using_OCILobArrayRead(OCISvcCtx *svchp, OCIError *errhp, OCILobLocator *lob)
{
    ub4 array_iter = 1;
    OCILobLocator *lobp_arr[1];
    oraub8 byte_amt_arr[1];
    oraub8 char_amt_arr[1];
    oraub8 offset_arr[1];
    void *bufp_arr[1];
    oraub8 bufl_arr[1];
    char buf[50];

    lobp_arr[0] = lob;
    byte_amt_arr[0] = 0;
    char_amt_arr[0] = UB4MAXVAL;
    offset_arr[0] = 1;
    bufp_arr[0] = buf;
    bufl_arr[0] = sizeof(buf);

    chk(OCILobArrayRead(svchp, errhp, &array_iter, lobp_arr, byte_amt_arr, char_amt_arr, offset_arr, bufp_arr, bufl_arr, OCI_ONE_PIECE, NULL, NULL, 0, SQLCS_IMPLICIT));
    printf("len=%d, data='%.*s'\n", (int)byte_amt_arr[0], (int)byte_amt_arr[0], buf);
}