title: error LNK2019 for ZLib sample code compiling
body: <p>I created win32 console application in vs2010 (without select the option of precompiled header). And I inserted the code below. but *.obj link failed. Could you provide me more information about the error. I searched MSDN, but still can't understand it.</p>
  
  <pre><code>#include &lt;stdio.h&gt;
  #include "zlib.h"
  
  // Demonstration of zlib utility functions
  
  unsigned long file_size(char *filename)
  {
     FILE *pFile = fopen(filename, "rb");
      fseek (pFile, 0, SEEK_END);
      unsigned long size = ftell(pFile);
      fclose (pFile);
      return size;
   }
  
   int decompress_one_file(char *infilename, char *outfilename)
   {
      gzFile infile = gzopen(infilename, "rb");
      FILE *outfile = fopen(outfilename, "wb");
      if (!infile || !outfile) return -1;
  
      char buffer[128];
      int num_read = 0;
      while ((num_read = gzread(infile, buffer, sizeof(buffer))) &gt; 0) {
         fwrite(buffer, 1, num_read, outfile);
         }
  
      gzclose(infile);
      fclose(outfile);
   }
  
   int compress_one_file(char *infilename, char *outfilename)
   {
      FILE *infile = fopen(infilename, "rb");
      gzFile outfile = gzopen(outfilename, "wb");
      if (!infile || !outfile) return -1;
  
      char inbuffer[128];
     int num_read = 0;
      unsigned long total_read = 0, total_wrote = 0;
      while ((num_read = fread(inbuffer, 1, sizeof(inbuffer), infile)) &gt; 0) {
         total_read += num_read;
         gzwrite(outfile, inbuffer, num_read);
      }
      fclose(infile);
      gzclose(outfile);
  
      printf("Read %ld bytes, Wrote %ld bytes, Compression factor %4.2f%%\n",
         total_read, file_size(outfilename),
         (1.0-file_size(outfilename)*1.0/total_read)*100.0);
   }        
   int main(int argc, char **argv)
   {
      compress_one_file(argv[1],argv[2]);
      decompress_one_file(argv[2],argv[3]);}
  </code></pre>
  
  <p>Output:</p>
  
  <pre><code>1&gt;------ Build started: Project: zlibApp, Configuration: Debug Win32 ------
  1&gt;  zlibApp.cpp
  1&gt;d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(15): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
  1&gt;          c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen'
  1&gt;d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(25): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
  1&gt;          c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen'
  1&gt;d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(40): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
  1&gt;          c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen'
  1&gt;d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(36): warning C4715: 'decompress_one_file' : not all control paths return a value
  1&gt;d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(57): warning C4715: 'compress_one_file' : not all control paths return a value
  1&gt;zlibApp.obj : error LNK2019: unresolved external symbol _gzclose referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z)
  1&gt;zlibApp.obj : error LNK2019: unresolved external symbol _gzread referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z)
  1&gt;zlibApp.obj : error LNK2019: unresolved external symbol _gzopen referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z)
  1&gt;zlibApp.obj : error LNK2019: unresolved external symbol _gzwrite referenced in function "int __cdecl compress_one_file(char *,char *)" (?compress_one_file@@YAHPAD0@Z)
  1&gt;D:\learning\cpp\cppVS2010\zlibApp\Debug\zlibApp.exe : fatal error LNK1120: 4 unresolved externals
  ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
  </code></pre>