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    <p>Multiple problems.</p> <p>Firstly, you need to check if inptr and outptr are valid by testing against NULL.</p> <p>Secondly, fscanf can return either EOF, 0 or > 0.</p> <p>If your input file doesn't contain valid input. </p> <p>Also there are problems in that you can get 3 ints read successfull, or 2 ints or 1 and the value of a, b and c are only optionally set.</p> <p>If no conversion took place on the input then the value of zero is returned in which case the while loop will exit.</p> <p>Also bear in mind that with the scanf style functions this input will succeed and return the value of 1.</p> <blockquote> <p>"1rubbish"</p> </blockquote> <p>I think what you may want is something like the following:</p> <pre><code>// Somewhere near the top #include &lt;stderr.h&gt; // ... other includes const char* inname = "trianglein.txt"; const char* outname = "triangleout.txt"; // Any other stuff // Inside main... // Initialization of pointer and opening of file trianglein.txt if ((inptr = fopen(inname,"r")) == 0){ fprintf(stderr, "Error opening file %s: %s", inname, strerror(inname)); return -1; } // Initialization of pointer and opening of file triangleout.txt if ((outptr = fopen(outname,"w")) == 0){ fprintf(stderr, "Error opening file %s: %s", outname, strerror(outname)); return -1; } int result; while(true){ result = fscanf(inptr,"%d %d %d",&amp;a, &amp;b, &amp;c); if (result == EOF) break; if (result &lt; 3) // Ignore incomplete lines continue; // do the normal stuff } </code></pre>
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    1. COAlthough the "testing against NULL" is semantically correct, and your code correctly uses `if(!inptr)`, the two don't match each other. An `if(input != NULL)` would explicitly match, but hardly anyone bothers. The idiom tends to be `if(inptr = fopen("trianglein.txt") ...`, using an assignment in the test.
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    2. COTrue, and I'd probably write it that way normally.
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