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POistream not working in DEV C++
 

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  1. POistream not working in DEV C++
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    <p>I'm using ifstream and ofstream operations in DEV c++ but they don't seem to work correctly. I've been trying to write a little prime generator code but it doesn't work :\ When I display fstream::tellg() at any point, it displays -1:</p> <pre><code>#include&lt;iostream&gt; #include&lt;math.h&gt; #include&lt;fstream&gt; using namespace std; int prime (unsigned long long n) { ifstream f1; ofstream f2; unsigned long long i,m,root; int flag=0; for(i=2;i&lt;=n;i++) { f1.open("prime2.txt",ios::binary); if(!f1.is_open()) { cout&lt;&lt;"NOT OPEN"; } cout&lt;&lt;f1.tellg()&lt;&lt;" "; //Displaying getpointer pos flag=0; root=(unsigned long long)sqrt(i); while(f1.read((char*)&amp;m,sizeof(m))) { if((i%m)==0) { flag=1; break; } if(m&gt;root) { break; } } f1.close(); if(!flag) { f2.open("prime2.txt",ios::app|ios::binary); f2.write((char*)&amp;i,sizeof(i)); cout&lt;&lt;i&lt;&lt;" "; //Displaying num being written f2.close(); } } return 1; } int main(int argc, char* argv[]) { prime(50); system("pause"); } </code></pre> <p>(I'm sorry, i just couldn't make the whole thing get in one codeblock. I guess theres something wrong with [code] tag?)</p> <p>Output:</p> <p><code>NOT OPEN-1 2 -1 3 -1 4 -1 5 -1 6 -1 7 -1 8 -1 9 -1 10 -1 11 -1 12 -1 13 -1 14 -1 15 -1 16 -1 17 -1 18 -1 19 -1 20 -1 21 -1 22 -1 23 -1 24 -1 25 -1 26 -1 27 -1 2 8 -1 29 -1 30 -1 31 -1 32 -1 33 -1 34 -1 35 -1 36 -1 37 -1 38 -1 39 -1 40 -1 41 -1 42 -1 43 -1 44 -1 45 -1 46 -1 47 -1 48 -1 49 -1 50 Press any key to continue . . . </code></p>
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    1. USArpit Tarang
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      1. VTDownMod
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    1. COPlease switch to a better IDE/compiler. Dev-C++ was buggy 3-4 years ago. Since then it hasn't had a single update. There is absolutely no reason to use that outmoded, buggy piece of junk. On Windows, Microsoft has a free version of their (very good) compiler and IDE in Visual C++ Express. There's also the free Code::Blocks if you want a non-Microsoft IDE. Just... don't... use.... Dev-C++.
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      1. USjalf
    2. COI fixed your code block formatting - you need the four space at the beginning of every line that's to continue the block. That all said, I agree strongly with jalf - stop using Dev-C++, because it's a pile of outdated junk.
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      1. USPhil Miller
    3. COFixed formatting for you. Indenting code with four spaces works just fine.
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      1. USJohnsyweb
 

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