title: c++ binary write or read
body: <p>I have a problem when I tried to make a conversion of a text to binary format:</p>
  
  <p>As described in the code below, it worked well for test3.txt or test4.txt, however, <code>fout3.write(str1.data() ,len);</code> doesn't work for test5.txt (WHICH REALLY puzzled me) so I used <code>fout3.write(reinterpret_cast&lt;char *&gt;(&amp; str1) ,len);</code> instead, and it worked well.</p>
  
  <pre><code>#include &lt;cassert&gt;
  #include &lt;iostream&gt;
  #include &lt;fstream&gt;
  #include &lt;string&gt;
  
  using namespace std;
  
  int main(void)
  {
     ofstream fout("test3.txt", ios::out | ios::binary);
     fout &lt;&lt; "ABC\n";
     fout.close();
  
     int test =  111;
     ofstream fout1("test4.txt", ios::out | ios::binary);
     fout1.write(reinterpret_cast&lt;char *&gt;(&amp;test), sizeof(int));
     fout1.close();
  
     int test2;
     ifstream fin("test4.txt", ios::in | ios::binary);
     fin.read(reinterpret_cast&lt;char *&gt;(&amp;test2), sizeof(int));
     cout &lt;&lt; test2 &lt;&lt; endl;
  
     string str1 = "ATEGWGEf";
     int len = str1.length();
     cout &lt;&lt; str1.data() &lt;&lt; endl;
     ofstream fout3("test6.txt", ios::out | ios::binary);
  // fout3.write(str1.data() ,len);
     fout3.write(reinterpret_cast&lt;char *&gt;(&amp; str1) ,len);
     fout3.close();
  
     string line;
     ifstream fin2("test6.txt",  ios::in | ios::binary);
     fin2.read(reinterpret_cast&lt;char *&gt;(&amp;line),300);
     cout &lt;&lt; line &lt;&lt; endl;
  
     return 0;
  }
  </code></pre>
  
  <p>But another question come to me. When I tried to read test6.txt, which was just wrote,
   it failed with error like this.</p>
  
  <pre><code>*** glibc detected *** ./binary_file.debug: double free or corruption (fasttop): 0x0000000001e4c260 ***
  ======= Backtrace: =========
  /lib64/libc.so.6[0x3155275366]
  /usr/lib64/libstdc++.so.6(_ZNSsD1Ev+0x39)[0x317209d4c9]
  ./binary_file.debug[0x4010f3]
  /lib64/libc.so.6(__libc_start_main+0xfd)[0x315521ecdd]
  ./binary_file.debug[0x400d69]
  ======= Memory map: ========
  ......................
  01e4a000-01e6b000 rw-p 00000000 00:00 0                                  [heap]
  3154a00000-3154a20000 r-xp 00000000 fd:00 3031286                        /lib64/ld-2.12.so
  3154c1f000-3154c20000 r--p 0001f000 fd:00 3031286                        /lib64/ld-2.12.so
  3154c20000-3154c21000 rw-p 00020000 fd:00 3031286                        /lib64/ld-2.12.so
  3154c21000-3154c22000 rw-p 00000000 00:00 0
  3155200000-3155389000 r-xp 00000000 fd:00 3033037                        /lib64/libc-2.12.so
  3155389000-3155588000 ---p 00189000 fd:00 3033037                        /lib64/libc-2.12.so
  3155588000-315558c000 r--p 00188000 fd:00 3033037                        /lib64/libc-2.12.so
  315558c000-315558d000 rw-p 0018c000 fd:00 3033037                        /lib64/libc-2.12.so
  315558d000-3155592000 rw-p 00000000 00:00 0
  3155600000-3155683000 r-xp 00000000 fd:00 3033062                        /lib64/libm-2.12.so
  3155683000-3155882000 ---p 00083000 fd:00 3033062                        /lib64/libm-2.12.so
  3155882000-3155883000 r--p 00082000 fd:00 3033062                        /lib64/libm-2.12.so
  3155883000-3155884000 rw-p 00083000 fd:00 3033062                        /lib64/libm-2.12.so
  3171c00000-3171c16000 r-xp 00000000 fd:00 3014674                        /lib64/libgcc_s-4.4.7-20120601.so.1
  3171c16000-3171e15000 ---p 00016000 fd:00 3014674                        /lib64/libgcc_s-4.4.7-20120601.so.1
  3171e15000-3171e16000 rw-p 00015000 fd:00 3014674                        /lib64/libgcc_s-4.4.7-20120601.so.1
  3172000000-31720e8000 r-xp 00000000 fd:00 1719247                        /usr/lib64/libstdc++.so.6.0.13
  31720e8000-31722e8000 ---p 000e8000 fd:00 1719247                        /usr/lib64/libstdc++.so.6.0.13
  31722e8000-31722ef000 r--p 000e8000 fd:00 1719247                        /usr/lib64/libstdc++.so.6.0.13
  31722ef000-31722f1000 rw-p 000ef000 fd:00 1719247                        /usr/lib64/libstdc++.so.6.0.13
  31722f1000-3172306000 rw-p 00000000 00:00 0
  7f1142209000-7f114220e000 rw-p 00000000 00:00 0
  7f114222d000-7f1142230000 rw-p 00000000 00:00 0
  7fff7ff9c000-7fff7ffb1000 rw-p 00000000 00:00 0                          [stack]
  7fff7ffff000-7fff80000000 r-xp 00000000 00:00 0                          [vdso]
  ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
  Aborted (core dumped)
  </code></pre>
  
  <p>Together with this error, I successfully convert binary test6.txt to texts by accident. I really want to know why and how to fix this bug.</p>
  
  <p>Thx!</p>