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POC++ Logic_error when using vector obtain from sqlite select statement
 

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  1. POC++ Logic_error when using vector obtain from sqlite select statement
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    <p>I tried to run my C++ code and tried debuging for the past 1 hour. I keep checking, but not sure what I'm doing wrong?</p> <p>The code will not have issue If I key a wrong user/password, but if I key correctly, whereas it's enter the logincheck=actionvalue, it will throws error as shown below.</p> <p>Here is a look of my database select statement:</p> <pre><code>root@ubuntu:/home/baoky/version1.2/Assignment 2# sqlite3 abeserver.db SQLite version 3.7.9 2011-11-01 00:52:41 Enter ".help" for instructions Enter SQL statements terminated with a ";" sqlite&gt; select * from abe_account; admin|Peter John|admin|password if (logincheck==actionvalue) </code></pre> <p>My code.cpp</p> <pre><code>#include &lt;iostream&gt; #include &lt;stdlib.h&gt; #include &lt;stdio.h&gt; #include &lt;signal.h&gt; #include &lt;sys/types.h&gt; #include &lt;sys/socket.h&gt; #include &lt;sys/un.h&gt; #include &lt;vector&gt; #include &lt;string&gt; #include &lt;fstream&gt; #include &lt;sqlite3.h&gt; #define DEFAULT_PROTOCOL 0 #ifndef AF_LOCAL #define AF_LOCAL AF_UNIX #endif #ifndef PF_LOCAL #define PF_LOCAL PF_UNIX #endif //g++ -o test test.cpp -lsqlite3 (sample compile with sqlite3) using namespace std; /* THIS IS SERVER CODE */ /* I WILL USE A TEMP FILE account.txt for basic login auth check */ int readLine (int fd, char* str) { int n; do /* Read characters until NULL or end-of-input */ { // ssize_t read (int fd, void *buf, size_t count); // if successful, read will: // a) stores data read into 'buf', and // b) returns the no. of bytes read // read returns zero if it reaches end-of-input n = read (fd, str, 1); /* Read one character */ } while (n &gt; 0 &amp;&amp; *str++ != 0); return (n &gt; 0); /* Return false if end-of-input */ } string readClient (int fd) { char str[2000]; while (readLine (fd, str)) /* Read lines until end-of-input */ return(string)str; /* return as string */ } std::vector&lt;std::string&gt; split(std::string const&amp; str, std::string const&amp; delimiters = "#") { std::vector&lt;std::string&gt; tokens; // Skip delimiters at beginning. string::size_type lastPos = str.find_first_not_of(delimiters, 0); // Find first "non-delimiter". string::size_type pos = str.find_first_of(delimiters, lastPos); while (string::npos != pos || string::npos != lastPos) { // Found a token, add it to the vector. tokens.push_back(str.substr(lastPos, pos - lastPos)); // Skip delimiters. Note the "not_of" lastPos = str.find_first_not_of(delimiters, pos); // Find next "non-delimiter" pos = str.find_first_of(delimiters, lastPos); } return tokens; } std::vector&lt;std::string&gt; split(std::string const&amp; str, char const delimiter) { return split(str,std::string(1,delimiter)); } int main() { int serverFd; int clientFd; int serverLen; int clientLen; int counter; string action; string actionvalue; string receiveClient; string sendClient; string department; string sline; string logincheck; ifstream myfile; struct sockaddr* serverSockAddrPtr; struct sockaddr* clientSockAddrPtr; struct sockaddr_un serverAddress; struct sockaddr_un clientAddress; //for handle zombie //to ignore SIGCHLD(death of child signal).The zombies will not be seen. signal(SIGCHLD, SIG_IGN); //zombies(defunct processes ps command in Linux will show defunct entries) cout &lt;&lt; "" &lt;&lt; endl; cout &lt;&lt; "Running server program 'ABEServer' ...... " &lt;&lt; endl; cout &lt;&lt; "" &lt;&lt; endl; // SOCKET CREATION PART - SERVER serverFd = socket (AF_LOCAL, SOCK_STREAM, DEFAULT_PROTOCOL); /* Set domain type */ serverAddress.sun_family = AF_LOCAL; /* Set name */ strcpy (serverAddress.sun_path, "ABEServer"); /* GET SIZE OF Server Addres */ serverLen = sizeof serverAddress; /* GET SIZE OF Client Addres */ clientLen = sizeof clientAddress; /* Get Server Sock Address Pointer*/ serverSockAddrPtr = (struct sockaddr *) &amp;serverAddress; /* Get Client Sock Address Pointer*/ clientSockAddrPtr = (struct sockaddr *) &amp;clientAddress; /* Create file */ unlink("ABEServer"); bind (serverFd, serverSockAddrPtr , serverLen); /* listen for connection */ listen (serverFd,5); cout &lt;&lt; "Server started"; cout &lt;&lt; "" &lt;&lt; endl; // SOCKET CREATION END - SERVER while (1) /* Loop forever */ { /* Accept a client connection */ clientFd = accept (serverFd, clientSockAddrPtr, (socklen_t*) &amp;clientLen); if (fork () == 0) /* Create child to send client */ { while(1) { sendClient = ""; //read client input receiveClient = readClient(clientFd); vector&lt;string&gt; x = split(receiveClient, '#'); action = x[0]; actionvalue = x[1]; if(action=="auth") { logincheck = ""; counter = 0; department = ""; //default sendClient value sendClient = "fail login#Invalid username/password."; sqlite3 *db; sqlite3_stmt * stmt; std::vector&lt; std::vector &lt; std:: string &gt; &gt; result; for( int i = 0; i &lt; 4; i++ ) result.push_back(std::vector&lt; std::string &gt;()); if (sqlite3_open("abeserver.db", &amp;db) == SQLITE_OK) { sqlite3_prepare( db, "SELECT * from abe_account;", -1, &amp;stmt, NULL );//preparing the statement sqlite3_step( stmt );//executing the statement while( sqlite3_column_text( stmt, 0 ) ) { for( int i = 0; i &lt; 4; i++ ) result[i].push_back( std::string( (char *)sqlite3_column_text( stmt, i ) ) ); sqlite3_step( stmt ); counter++; } //close connection to db and finalize sql statement sqlite3_finalize(stmt); sqlite3_close(db); //username:password // using first record to check for ( int i = 0; i &lt; counter; i ++) { //result[column][row] logincheck = result[0][i] + ":" + result[3][i]; department = result[2][i]; } if (logincheck==actionvalue) { //send back in format of login done, login message, department level sendClient = "login done#Successfully Login"; break; } result.clear(); } }//end if auth write (clientFd, sendClient.c_str(), strlen (sendClient.c_str()) + 1); }//end while }//end if fork else { close (clientFd); /* Close the client descriptor */ }//end else }//end while outer return 0; } </code></pre> <p>Error Message:</p> <pre><code>Username &gt; admin Password &gt; password terminate called after throwing an instance of 'std::logic_error' what(): basic_string::_S_construct null not valid Segmentation fault (core dumped) </code></pre>
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    1. PTQuestion
    1. USLOZ
    1. USuser1595932
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
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      1. POC++ Logic_error when using vector obtain from sqlite select statement
      1. This table or related slice is empty.
      1. VTApproveEditSuggestion
    1. COLooks like you're trying to assign a null pointer to std::string.
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      1. POC++ Logic_error when using vector obtain from sqlite select statement
      1. USCaptain Obvlious
    2. COpossible duplicate of [How to avoid the error: terminate called after throwing an instance of 'std::logic_error' what(): basic_string::_S_construct null not valid](http://stackoverflow.com/questions/11705886/how-to-avoid-the-error-terminate-called-after-throwing-an-instance-of-stdlog)
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      1. POC++ Logic_error when using vector obtain from sqlite select statement
      1. USJonathan Wakely
    3. COYou should use a debugger to find which line throws the exception, and fix it. As @CaptainObvlious said, that exception means you're constructing a `std::string` with a null pointer.
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      1. POC++ Logic_error when using vector obtain from sqlite select statement
      1. USJonathan Wakely
 

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