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POHow do I overwrite a single byte in a binary file using fseek() and fwrite()?
 

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  1. POHow do I overwrite a single byte in a binary file using fseek() and fwrite()?
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    <p>I am trying to overwrite a single byte in a binary file. I am using <code>fseek()</code> to set the stream position indicator to the byte that I want to overwrite. Then I am calling to <code>fwrite()</code> with a new byte in that location. Somehow the other bytes in the file are being affected. Heres some code:</p> <pre><code>bool x = 1; bool y = 0; bool z = 1; /* WRITE 101 to file */ FILE *ff = fopen(file, "wb"); fwrite(&amp;x, sizeof(x), 1, ff); fwrite(&amp;y, sizeof(y), 1, ff); fwrite(&amp;z, sizeof(y), 1, ff); fclose(ff); bool x_r, y_r, z_r; /* READ from file */ ff = fopen(file, "rb"); fread(&amp;x_r, sizeof(x_r), 1, ff); fread(&amp;y_r, sizeof(y_r), 1, ff); fread(&amp;z_r, sizeof(z_r), 1, ff); fclose(ff); /* PRINT to standard output */ cout &lt;&lt; x_r &lt;&lt; y_r &lt;&lt; z_r &lt;&lt; endl; // OUTPUT: 101 bool overwrite = 1; /* OVERWRITE */ ff = fopen(file, "wb"); fseek(ff, 1, SEEK_SET); fwrite(&amp;overwrite, sizeof(overwrite),1 , ff); fclose(ff); /* READ from file */ ff = fopen(file, "rb"); fread(&amp;x_r, sizeof(x_r), 1, ff); fread(&amp;y_r, sizeof(y_r), 1, ff); fread(&amp;z_r, sizeof(z_r), 1, ff); fclose(ff); /* PRINT to standard output */ cout &lt;&lt; x_r &lt;&lt; y_r &lt;&lt; z_r &lt;&lt; endl; // OUPUT 011; I was expecting 111 </code></pre> <p>The above code basically writes three bytes of data to a file. 101. Then I use fseek() to set to reposition the stream indicator to point to the second byte. But calling fwrite() to overwrite the second byte from 0 to 1 is changing the first byte as well. The expected output is 111, but I am getting 011.</p> <p>Any ideas why this is happening? I tried putc as well, but that didn't work out either. Any help would be appreciated.</p>
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    1. USRakib Ansary
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    1. COIn C++, you are guaranteed that 1 <= sizeof( bool ) <= sizeof( long ). You should not assume that sizeof( bool ) == 1.
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      1. POHow do I overwrite a single byte in a binary file using fseek() and fwrite()?
      1. USWilliam Pursell
 

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