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POTrouble with Strings
 

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  1. POTrouble with Strings
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    <p>I am currently debugging a sizable program. When I come to the following line of code:</p> <pre><code>value-&gt;binary_string = value_it-&gt;binary_string.substr(range-&gt;msb-&gt;value, range-&gt;size); </code></pre> <p>The program does not behave correctly. Here value is a pointer to a struct with a member named binary_string with type std::string. When I reach this line while debugging, I see that:</p> <pre><code>value_it-&gt;binary_string = "00000000000000000000000000000111" range-&gt;msb-&gt;value = 0 range-&gt;size = 32 </code></pre> <p>After this line of code executes, value->binary_string is empty! I have even changed the line to</p> <pre><code>value-&gt;binary_string = value_it-&gt;binary_string </code></pre> <p>and it still fails!</p> <p>When I reach this line while debugging, my program is using about 100 Mb of memory, so I don't think it is a memory issue (though I am running Valgrind as we speak to verify this). I am using Ubuntu 11.10, g++-4.6 and libstdc++6.</p> <p>Has anyone encountered something like this before? I have no idea why my strings aren't working!</p> <p>Thanks,</p> <p>Sam</p> <p>EDIT1:</p> <p>The type of value is NumberInst, defined below:</p> <pre><code>typedef std::string String; struct NumberInst { unsigned size; bool signed_; String binary_string; bool valid; unsigned value; NumberInst(); }; </code></pre> <p>EDIT2:</p> <p>It looks like I've narrowed down the search a little bit. While debugging, I tried a few print commands:</p> <pre><code>print value_it-&gt;binary_string "00000000000000000000000000000111" print value_it-&gt;binary_string[31] '1' print value_it-&gt;binary_string.substr(0, String::npos) "" print value_it-&gt;binary_string.substr(0, 1) "" </code></pre> <p>It seems that substr is not working properly in this context. However, when I tested substr in my main function, it seemed to work okay.</p>
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    1. USSam Hertz
    1. USSam Hertz
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    1. COHave you verified that `value` is allocated correctly (and hasn't been freed)?
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      1. USYaniro
    2. CO@Yaniro I just checked. The new call is just before that line of code and when I step into the new call I reach the constructor for value. Also, I tested a call to push_back, which seems to work properly.
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      1. USSam Hertz
    3. COCheck out this copy on write stuff: http://en.wikipedia.org/wiki/Copy-on-write... it could be that the two string are using the same buffer until you change one of them if i understand correctly...
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