sqlite3_exec function ignores sql buildup function value

Question

I got the following sql_buildup_method... code is bit dirty but that s not the case

char *build_up_sql(char *inputName,char *inputMessage)
{
   char firstPartStatement[1064] ="INSERT INTO User (name, msg) VALUES (";
    char *endPartStatement =");";
    char *lightener = "'";  
    char *statement;

strcat(firstPartStatement,lightener);
strcat(firstPartStatement,inputName);
strcat(firstPartStatement,lightener);
strcat(firstPartStatement,",");
strcat(firstPartStatement,lightener);
strcat(firstPartStatement,inputMessage);
strcat(firstPartStatement,lightener);
strcat(firstPartStatement,endPartStatement);

statement = firstPartStatement; 

return statement;

}

void create_input(sqlite3 *handler,char *inputName,char *inputMessage)
{
    char *sql;

    sql = build_up_sql(inputName,inputMessage);
 // sql ="INSERT INTO User (name, msg) VALUES ('Susanne','hi all');";   
    printf("%s\n",sql);
    sqlite3_exec(handler,sql, NULL, NULL, NULL);
}

the printf gives the output: INSERT INTO User (name, msg) VALUES ('Susanne','hi all'); which is totally fine ... but the sqlite3_exec ignores it and isn't generating new database input .... if I leave the line sql ="INSERT INTO User (name, msg) VALUES ('Susanne','hi all');"; in the code the sqlite3_exec just works fine .... also putting everything in one function also solved the problem, but this shouldn't be an option.....

Some programmer dude · Accepted Answer · 2012-07-18 09:17:26Z

1

The problem here is that you are returning a pointer to a local variable, which is undefined behavior. When build_up_sql returns, the space on the stack for the local variables are reused.

The best solution is probably to add a parameter to build_up_sql that you use to put the string in. Something like:

char *build_up_sql(char *inputName, char *inputMessage, char *outputSql)
{
    const char firstPartStatement[] = "INSERT INTO User (name, msg) VALUES (";
    const char endPartStatement[] = ");";
    const char lightener[] = "'";

    strcpy(outputSql, firstPartStatement);
    strcat(outputSql,lightener);
    strcat(outputSql,inputName);
    strcat(outputSql,lightener);
    strcat(outputSql,",");
    strcat(outputSql,lightener);
    strcat(outputSql,inputMessage);
    strcat(outputSql,lightener);
    strcat(outputSql,endPartStatement);

    return outputSql;
}

void create_input(sqlite3 *handler, char *inputName, char *inputMessage)
{
    char sql[1024];

    char *sqlstr = build_up_sql(inputName, inputMessage, sql);

    printf("%s\n", sqlstr);
    sqlite3_exec(handler, sqlstr, NULL, NULL, NULL);
}

answered Jul 18, 2012 at 9:17

Some programmer dude

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3 Comments

Fendrix Over a year ago

it works....thank u very much... I really appreciate it.... I am just curious... I understand what you mean, but why do I get in the printf the correct String ?

Some programmer dude Over a year ago

@Fendrix Pure luck it works! :) Probably the stack hasn't been overwritten yet, so that's why it works in the printf call, but that call do overwrite the stack so the next call will not work.

Fendrix Over a year ago

thx... if I would have a reputation score over 15 I would vote ur answer as usefull ... but I am still on 14, so sorry ....:)

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