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POTo copy files in binary mode,why it doesn't work when we read to and write from a character variable?
 

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  1. POTo copy files in binary mode,why it doesn't work when we read to and write from a character variable?
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    <p>The following program is intended to make a copy of one <strong>.exe</strong> application file.But just one little thing determines whether it indeed gives me a proper copy of the intended file <strong>RealPlayer.exe</strong> or gives me a corrupted file.</p> <p>What I do is read from the source file in binary mode and write to the new copy in the same mode.For this I use a variable <code>ch</code>.But if <code>ch</code> is of type <code>char</code>, I get a corrupted file which has a size of few bytes while the original file is <strong>26MB</strong>.But if I change the type of <code>ch</code> to <code>int</code>, the program works fine and gives me the exact copy of <strong>RealPlayer.exe</strong> sized <strong>26MB</strong>.So let me ask two questions that arise from this premise.I would appreciate if you can answer both parts:</p> <p><strong>1)</strong> Why does using type <code>char</code> for <code>ch</code> mess things up while <code>int</code> type works?What is wrong with <code>char</code> type?After all, shouldn't it read byte by byte from the original file(as <code>char</code> is one byte itself) and write it byte by byte to the new copy file?After all isn't what the <code>int</code> type does,ie, read 4 bytes from original file and then write that to the copy file?Why the difference between the two?</p> <p><strong>2)</strong> Why is the file so small-sized compared to original file if we use <code>char</code> type for <code>ch</code>?Let's forget for a moment that the copied file is corrupt to begin with and focus on the size.Why is it that the size is so small if we copy character by character (or byte by byte), but is big(original size) when we copy "integer by integer" (or 4-bytes by 4-bytes)?</p> <p>I was suggested by a friend to simply stop asking questions and use <code>int</code> because it works while <code>char</code> doesn't!!.But I need to understand what's going on here as I see a serious lapse in my understanding in this matter.Your detailed answers are much sought.Thanks.</p> <pre><code>#include&lt;stdio.h&gt; #include&lt;stdlib.h&gt; int main() { char ch; //This is the cause of problem //int ch; //This solves the problem FILE *fp,*tp; fp=fopen("D:\\RealPlayer.exe","rb"); tp=fopen("D:\\copy.exe","wb"); if(fp==NULL||tp==NULL) { printf("Error opening files"); exit(-1); } while((ch=getc(fp))!=EOF) putc(ch,tp); fclose(fp); fclose(tp); } </code></pre>
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    1. USRüppell's Vulture
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    1. CO@JimBalter Thanks.That was a helpful link.
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    2. COSee also http://msdn.microsoft.com/en-us/library/yeby3zcb%28vs.71%29.aspx relating to some of your comments below. On Windows systems, in text mode only, ctrl-Z (026) will be interpreted as end-of-file. What that means is that getc will return EOF (-1), *not* ctrl-Z, if a ctrl-Z is encountered. Which means that opening binary files in text mode on Windows systems is a very bad thing to do.
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      1. USJim Balter
    3. CO@JimBalter Thanks again.If you've ever found any of my comments as against SO rules & FAQ,then I apologize to you.
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