2009/7/3 chandan <[email protected]>:
> 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
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