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Thread: My code is going out of bounds

  1. #1
    Join Date
    Nov 2014
    Posts
    17

    My code is going out of bounds

    I am really unsure how to keep within the boundries and still perform the function I need.
    My code functions normal when I have both categories 'buy' and 'sell' in the queue which is my main goal and I should be clocked out on this function BUT,,,
    If the queue is missing all 'sell' data, it segment faults.
    I don't want to change any of the functionality, just get rid of the segment fault error.
    It appears b < buydat.size() and buydat[b+1] are in conflict.
    The purpose of the algorithm is capture the record sets in groups of 7 from data coming in from the www as strings. In that group/set, I pattern match for the string 'Buy' and if true, insert record into vector for processing. I also need the price (y = 3)

    How do I capture buydat[2] and buydat[3] in groups of 7 without a segment fault?




    Code:
    void buymngr(){
            //vector defs
            vector<std::string> buydat;
            vector<std::string> markdat;
            vector<std::string> pricedat;
            vector<std::string> qworkcoin;
    
            buydat = getmyData();
            markdat = getmarketbuyData();
            cout << "Bork!" << endl;
    		//This if statement was put here to try and prevent running code if missing data (seg fault patch)
    		//It does not work and if category 'sell' is missing, it will fail to 'True' and run anyway then segment fault
            //if(!buydat.empty()){
            if(buydat[2] == std::string("Buy")){
                    cout << "Bork2!" << endl;
                    for(int b = 2; b < buydat.size(); b+=7){
                            int y = 3;  y+=7;
                            if ( buydat[b] == "Buy" ) {
                                    pricedat.push_back(buydat[b+1]);
    								//segment fault here
                                    qworkcoin.push_back(buydat[y+1]);
                            }
    				}
    		}


    gentoo-mini # cat getmyData.h
    Code:
    #include <vector>
    using namespace std;
    
    vector<string> getmyData()
    {
            FILE *mydfp = popen("php getMyorders.php 155", "r");
            if (mydfp == NULL) perror ("Error opening file");
            char mydbuff[BUFSIZ];
            vector<string> vrecords;
            while(fgets(mydbuff, sizeof(mydbuff), mydfp) != NULL){
                    size_t n = strlen(mydbuff);
                    //clean '\0' from fgets
                    if (n && mydbuff[n - 1] == '\n') mydbuff[n - 1] = '\0';
                    if (mydbuff[0] != '\0') vrecords.push_back(mydbuff);
                    //if (mydbuff[0] != '\0') vrecords.push_back("0.001");
                    //vrecords.push_back("0.003");
                    //vrecords.push_back("0.0032");
                    //vrecords.push_back("0.0033");
                    //vrecords.push_back("0.0034");
            }
            cout << "I got my own data" << endl;
            return vrecords;
    }

    When one buy and one sell are sitting in the queue. Code functions as expected:

    gentoo-mini # ./masterMain
    Code:
    I got my own data
    I just got market buy data
    Bork!
    Bork2!
    You 'do' have buy string match data!
    my max price is 0.00492975 at position 0
    market max price is 0.00560504 at position 0
    Highest is market!0.005605 0.00100000
    php buycoin.php 155 0.005605 0.00100000 Command
    0.005605 0.00100000 sendbuy
    0.005605 0.00100000 mkbuybuff
    0.00560505 *biggestMark
    0.00100000
    You bought coins, you are now top buyer
    I got my own data
    I just got market sell data
    my min price is 0.00760479 at position 0
    market min price is 0.00564973 at position 0
    Lowest is market!php sellcoin.php 155 0.00564972
    0.00564972
    226250684


    Data from the www following is as expected:

    gentoo-mini # php getMyorders.php 155
    Code:
    224122032
    2014-12-21 18:17:43
    Buy
    0.00492975
    0.00010000
    0.00010000
    0.00000049
    226250651
    2014-12-26 10:56:48
    Buy
    0.00560500
    0.00100000
    0.00100000
    0.00000561
    226250684
    2014-12-26 10:56:55
    Sell
    0.00564972
    0.00100000
    0.00100000
    0.00000565
    226250585
    2014-12-26 10:56:31
    Sell
    0.00760479
    0.00100000
    0.00100000
    0.00000760
    BUT,,,
    If I clear sell data and have only buy data in the queue, I get a segment fault:

    gentoo-mini # ./masterMain
    Code:
    I got my own data
    I just got market buy data
    Bork!
    Bork2!
    Segmentation fault
    Data sitting in queue is as follows:

    gentoo-mini # php getMyorders.php 155
    Code:
    224122032
    2014-12-21 18:17:43
    Buy
    0.00492975
    0.00010000
    0.00010000
    0.00000049

    gdb

    gentoo-mini # gdb masterMain
    Code:
    GNU gdb (Gentoo 7.7.1 p1) 7.7.1
    Copyright (C) 2014 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
    and "show warranty" for details.
    This GDB was configured as "x86_64-pc-linux-gnu".
    Type "show configuration" for configuration details.
    For bug reporting instructions, please see:
    <http://bugs.gentoo.org/>.
    Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.
    For help, type "help".
    Type "apropos word" to search for commands related to "word"...
    Reading symbols from masterMain...done.
    (gdb) run
    Starting program: masterMain
    warning: Could not load shared library symbols for linux-vdso.so.1.
    Do you need "set solib-search-path" or "set sysroot"?
    I got my own data
    I just got market buy data
    Bork!
    Bork2!
    
    Program received signal SIGSEGV, Segmentation fault.
    0x00007ffff7b9355b in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) ()
       from /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/libstdc++.so.6
    (gdb) bt
    #0  0x00007ffff7b9355b in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) ()
       from /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/libstdc++.so.6
    #1  0x0000000000404ffc in __gnu_cxx::new_allocator<std::string>::construct<std::string<std::string const&> > (this=0x7fffffffbfc0, __p=0x60a1b0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/ext/new_allocator.h:120
    #2  0x0000000000404b19 in std::allocator_traits<std::allocator<std::string> >::_S_construct<std::string<std::string const&> >(std::allocator<std::string>&, std::allocator_traits<std::allocator<std::string> >::__construct_helper*, (std::string<std::string const&>&&)...) (__a=..., __p=0x60a1b0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/bits/alloc_traits.h:254
    #3  0x0000000000404123 in std::allocator_traits<std::allocator<std::string> >::construct<std::string<std::string const&> >(std::allocator<std::string>&, std::string<std::string const&>*, (std::string<std::string const&>&&)...) (__a=...,
        __p=0x60a1b0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/bits/alloc_traits.h:393
    #4  0x00000000004041ad in std::vector<std::string, std::allocator<std::string> >::_M_emplace_back_aux<std::string const&> (this=0x7fffffffbfc0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/bits/vector.tcc:408
    #5  0x0000000000403a69 in std::vector<std::string, std::allocator<std::string> >::---Type <return> to continue, or q <return> to quit---   q
    Quit
    (gdb)
    #0  0x00007ffff7b9355b in std::basic_string<char, std::char_traits<char>, std::allocator<char> >::basic_string(std::string const&) ()
       from /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/libstdc++.so.6
    #1  0x0000000000404ffc in __gnu_cxx::new_allocator<std::string>::construct<std::string<std::string const&> > (this=0x7fffffffbfc0, __p=0x60a1b0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/ext/new_allocator.h:120
    #2  0x0000000000404b19 in std::allocator_traits<std::allocator<std::string> >::_S_construct<std::string<std::string const&> >(std::allocator<std::string>&, std::allocator_traits<std::allocator<std::string> >::__construct_helper*, (std::string<std::string const&>&&)...) (__a=..., __p=0x60a1b0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/bits/alloc_traits.h:254
    #3  0x0000000000404123 in std::allocator_traits<std::allocator<std::string> >::construct<std::string<std::string const&> >(std::allocator<std::string>&, std::string<std::string const&>*, (std::string<std::string const&>&&)...) (__a=...,
        __p=0x60a1b0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/bits/alloc_traits.h:393
    #4  0x00000000004041ad in std::vector<std::string, std::allocator<std::string> >::_M_emplace_back_aux<std::string const&> (this=0x7fffffffbfc0)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/bits/vector.tcc:408
    #5  0x0000000000403a69 in std::vector<std::string, std::allocator<std::string> >::---Type <return> to continue, or q <return> to quit---
    push_back (this=0x7fffffffbfc0,
        __x=<error reading variable: Cannot access memory at address 0xfffffffffffffff2>)
        at /usr/lib/gcc/x86_64-pc-linux-gnu/4.8.3/include/g++-v4/bits/stl_vector.h:911
    #6  0x0000000000401e62 in buymngr () at buymngr.h:38    (actually pointing to line 18 -> qworkcoin.push_back(buydat[y+1]);))
    #7  0x000000000040329f in main () at masterMain.cpp:25

  2. #2
    Join Date
    Nov 2014
    Posts
    17

    Re: My code is going out of bounds

    this was posted to the wrong section :/

  3. #3
    Join Date
    Jul 2013
    Posts
    576

    Re: My code is going out of bounds

    Quote Originally Posted by tunage View Post
    How do I capture buydat[2] and buydat[3] in groups of 7 without a segment fault?
    By applying stepwise refinement.

    Develop you code in small increments from start to finish. Make sure it works as intended in each step.

    The worst thing you can do is be sitting with a pile of crappy code having no clue, like now.
    Last edited by razzle; December 26th, 2014 at 06:14 PM.

  4. #4
    Join Date
    Nov 2014
    Posts
    17

    Re: My code is going out of bounds

    Quote Originally Posted by razzle View Post
    By applying stepwise refinement.

    Develop you code in small increments from start to finish. Make sure it works as intended in each step.

    The worst thing you can do is be sitting with a pile of crappy code having no clue, like now.
    Thank you very little!
    I won't remember that...

  5. #5
    Join Date
    Jul 2013
    Posts
    576

    Re: My code is going out of bounds

    Quote Originally Posted by tunage View Post
    Thank you very little!
    I won't remember that...
    That's too bad because then you're a programmer without future.

    It's so simple it almost hurts. You start with a small working program. Then you develop it in small working steps. And you end up with a big working program.

    It's called the principle of Stepwise Refinement and if you apply it consistently you'll soon be guru programmer.
    Last edited by razzle; December 26th, 2014 at 08:59 PM.

  6. #6
    2kaud's Avatar
    2kaud is offline Super Moderator Power Poster
    Join Date
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    Location
    England
    Posts
    7,113

    Re: My code is going out of bounds

    It appears b < buydat.size() and buydat[b+1] are in conflict.
    Correct. buydat[] has a range of 0 to size() - 1. So if size is 10, buydat[] has a range of 0 to 9. So in this case if b is 9, b is less than .size() (so the test is true) but b + 1 is out of bounds (gives segment fault) as buydat[10] is not valid.

    The 'easy' solution could be
    Code:
    for(int b = 2; b < buydat.size() - 1; b+=7){
    This will terminate the loop when b is less than .size() - 1, so now b + 1 is a valid index into buydat[].

    PS. When trying to find run-time issues with a program use the debugger to trace through the program to see values of variables etc when the code doesn't execute as expected.
    All advice is offered in good faith only. All my code is tested (unless stated explicitly otherwise) with the latest version of Microsoft Visual Studio (using the supported features of the latest standard) and is offered as examples only - not as production quality. I cannot offer advice regarding any other c/c++ compiler/IDE or incompatibilities with VS. You are ultimately responsible for the effects of your programs and the integrity of the machines they run on. Anything I post, code snippets, advice, etc is licensed as Public Domain https://creativecommons.org/publicdomain/zero/1.0/ and can be used without reference or acknowledgement. Also note that I only provide advice and guidance via the forums - and not via private messages!

    C++17 Compiler: Microsoft VS2019 (16.6.0)

  7. #7
    Join Date
    Nov 2014
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    17

    Re: My code is going out of bounds

    Quote Originally Posted by razzle View Post
    By applying stepwise refinement.

    Develop you code in small increments from start to finish. Make sure it works as intended in each step.

    The worst thing you can do is be sitting with a pile of crappy code having no clue, like now.
    I had asked a very specific question on the mechanics and you provided a very abstract and theoretical response, a very condescending one at that.
    Personally I find the rubber duckie method to be far more robust and professional http://en.wikipedia.org/wiki/Rubber_duck_debugging but the only issue is, what was coming from his quacker was trash. I was looking at it 'mechanically' wrong.
    Now, the gentleman below you did a superior job of providing a 'functional' response that answers many of the questions I had and probably will assist many readers..

  8. #8
    GCDEF is offline Elite Member Power Poster
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    Re: My code is going out of bounds

    Quote Originally Posted by tunage View Post
    I had asked a very specific question on the mechanics and you provided a very abstract and theoretical response, a very condescending one at that.
    Personally I find the rubber duckie method to be far more robust and professional http://en.wikipedia.org/wiki/Rubber_duck_debugging but the only issue is, what was coming from his quacker was trash. I was looking at it 'mechanically' wrong.
    Now, the gentleman below you did a superior job of providing a 'functional' response that answers many of the questions I had and probably will assist many readers..
    Given that you had to ask how to debug an array out of bounds question, your preferred debugging method isn't really of much interest. You've got some seriously good and experienced programmers helping you for free. If you plan on using the forum regularly, you'll find being snappish isn't going to get you very far.

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