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List:       sqlite-users
Subject:    Re: [sqlite] Value returned by sqlite3_column_bytes for strings
From:       chandan <chandan.babu () globaledgesoft ! com>
Date:       2009-07-03 9:53:24
Message-ID: 4A4DD244.2080806 () globaledgesoft ! com
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Thanks for the reply!

Simon Davies wrote:
> 2009/7/3 chandan <chandan.babu@globaledgesoft.com>:
>   
>> Hi all,
>>    Consider the following scenario,
>>    1. A table contains a column of type "text".
>>    2. The value of this column for the first row is say "linux".
>>
>> If we execute the SQL statement: "select name from some_tbl where id = ?"
>> using sqlite3_step() API, then what is the value returned by
>> sqlite3_column_bytes(). Does the count include the '\0' byte (count ==
>> 6). If it does not include the '\0' byte the count should be 5.
>>
>> I executed the following program:
>>
>> /******************************************************************************/
>> #include <stdio.h>
>> #include <stdint.h>
>> #include <stdlib.h>
>> #include <string.h>
>> #include "sqlite3.h"
>>
>> const char *update_db = "update some_tbl set name = ? where id = ?";
>> const char *read_db = "select name from some_tbl where id = ?";
>>
>> int32_t main(int argc, char *argv[])
>> {
>>    sqlite3_stmt *stmt;
>>    sqlite3 *db;
>>    int32_t num_bytes;
>>    char buf[100];
>>    int32_t ret;
>>
>>    if (argc != 2) {
>>        fprintf(stderr, "Usage: %s <database name>\n", argv[0]);
>>        goto out1;
>>    }
>>
>>    ret = sqlite3_initialize();
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "Unable to initialize db.\n");
>>        goto out1;
>>    }
>>
>>    ret = sqlite3_open(argv[1], &db);
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "Unable to open database.\n");
>>        goto out2;
>>    }
>>
>>    stmt = NULL;
>>    ret = sqlite3_prepare_v2(db, update_db, strlen(update_db) + 1,
>>                 &stmt, NULL);
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "sqlite3_prepare_v2: %s.\n",
>>            sqlite3_errmsg(db));
>>        goto out3;
>>    }
>>
>>    ret = sqlite3_bind_text(stmt, 1, "linux", strlen("linux") + 1,
>>                SQLITE_TRANSIENT);
>>     
>
> This will insert 6 bytes into the db - includes the trailing '\0'
>
>   
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "sqlite3_bind_text: %s.\n",
>>            sqlite3_errmsg(db));
>>        goto out4;
>>    }
>>
>>    ret = sqlite3_bind_int64(stmt, 2, 1);
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "sqlite3_bind_int64: %s.\n",
>>            sqlite3_errmsg(db));
>>        goto out4;
>>    }
>>
>>    ret = sqlite3_step(stmt);
>>    if (ret != SQLITE_DONE) {
>>        fprintf(stderr, "sqlite3_step: %s.\n",
>>            sqlite3_errmsg(db));
>>        goto out4;
>>    }
>>
>>    ret = sqlite3_finalize(stmt);
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "sqlite3_finalize: %s.\n",
>>            sqlite3_errmsg(db));
>>    }
>>
>>    stmt = NULL;
>>    ret = sqlite3_prepare_v2(db, read_db, strlen(read_db) + 1, &stmt,
>>                 NULL);
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "sqlite3_prepare_v2: %s.\n",
>>            sqlite3_errmsg(db));
>>        goto out3;
>>    }
>>
>>    ret = sqlite3_bind_int64(stmt, 1, 1);
>>    if (ret != SQLITE_OK) {
>>        fprintf(stderr, "sqlite3_bind_int64: %s.\n",
>>            sqlite3_errmsg(db));
>>        goto out4;
>>    }
>>
>>    ret = sqlite3_step(stmt);
>>    if (ret != SQLITE_ROW) {
>>        fprintf(stderr, "sqlite3_step: %s.\n",
>>            sqlite3_errmsg(db));
>>        goto out4;
>>    }
>>
>>    num_bytes = sqlite3_column_bytes(stmt, 0);
>>    printf("*** num_bytes = %d ***\n", num_bytes);
>>
>>    memcpy(buf, sqlite3_column_text(stmt, 0), num_bytes);
>>    printf("*** buf = %s ***\n", buf);
>>
>>    exit(0);
>>
>>  out4:
>>    ret = sqlite3_finalize(stmt);
>>  out3:
>>    ret = sqlite3_close(db);
>>  out2:
>>    ret = sqlite3_shutdown();
>>  out1:
>>    exit(1);
>> }
>> /*****************************************************************************/
>>
>>
>> The output shows that sqlite3_column_bytes() returns a count value that
>> includes the '\0'. Please correct me if I am arriving at the wrong
>> conclusion.
>>     
>
> This is what I would expect given that you are inserting a string that
> includes the '\0'. Your initial statement that the db contains 'linux'
> is wrong; it contains 'linux\0'.
>
> Regards,
> Simon
> _______________________________________________
> sqlite-users mailing list
> sqlite-users@sqlite.org
> http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
>
>   

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