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POfgetpos() behaviour depends on newline character
 

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  1. POfgetpos() behaviour depends on newline character
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    <p>Consider these two files:</p> <p>file1.txt (Windows newline)</p> <pre><code>abc\r\n def\r\n </code></pre> <p>file2.txt (Unix newline)</p> <pre><code>abc\n def\n </code></pre> <p>I've noticed that for the file2.txt, the position obtained with <code>fgetpos</code> is not incremented correctly. I'm working on Windows.</p> <p>Let me show you an example. The following code:</p> <pre><code>#include&lt;cstdio&gt; void read(FILE *file) { int c = fgetc(file); printf("%c (%d)\n", (char)c, c); fpos_t pos; fgetpos(file, &amp;pos); // save the position c = fgetc(file); printf("%c (%d)\n", (char)c, c); fsetpos(file, &amp;pos); // restore the position - should point to previous c = fgetc(file); // character, which is not the case for file2.txt printf("%c (%d)\n", (char)c, c); c = fgetc(file); printf("%c (%d)\n", (char)c, c); } int main() { FILE *file = fopen("file1.txt", "r"); printf("file1:\n"); read(file); fclose(file); file = fopen("file2.txt", "r"); printf("\n\nfile2:\n"); read(file); fclose(file); return 0; } </code></pre> <p>gives such result:</p> <pre><code>file1: a (97) b (98) b (98) c (99) file2: a (97) b (98)   (-1)   (-1) </code></pre> <p>file1.txt works as expected, while file2.txt behaves strange. To explain what's wrong with it, I tried the following code:</p> <pre><code>void read(FILE *file) { int c; fpos_t pos; while (1) { fgetpos(file, &amp;pos); printf("pos: %d ", (int)pos); c = fgetc(file); if (c == EOF) break; printf("c: %c (%d)\n", (char)c, c); } } int main() { FILE *file = fopen("file1.txt", "r"); printf("file1:\n"); read(file); fclose(file); file = fopen("file2.txt", "r"); printf("\n\nfile2:\n"); read(file); fclose(file); return 0; } </code></pre> <p>I got this output:</p> <pre><code>file1: pos: 0 c: a (97) pos: 1 c: b (98) pos: 2 c: c (99) pos: 3 c: (10) pos: 5 c: d (100) pos: 6 c: e (101) pos: 7 c: f (102) pos: 8 c: (10) pos: 10 file2: pos: 0 c: a (97) // something is going wrong here... pos: -1 c: b (98) pos: 0 c: c (99) pos: 1 c: (10) pos: 3 c: d (100) pos: 4 c: e (101) pos: 5 c: f (102) pos: 6 c: (10) pos: 8 </code></pre> <p>I know that <code>fpos_t</code> is not meant to be interpreted by coder, because it's depending on implementation. However, the above example explains the problems with <code>fgetpos</code>/<code>fsetpos</code>.</p> <p>How is it possible that the newline sequence affects the internal position of the file, even before it encounters that characters?</p>
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    1. USmiloszmaki
    1. USmiloszmaki
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    1. COBtw changing "rt" to "rb" fixes the problem but it's not a solution for me, because I have to read some numbers and strings from the file using fscanf as well.
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      1. USmiloszmaki
    2. COI've tried both IDE's: VS C++ 2010 and Dev-cpp.
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      1. USmiloszmaki
    3. COCan you add another line of text to your two files. I suspect that it will "correct itself", in the sense that `\r` isn't counted as a character, but when you get to the second line, the position will jump one character. In other words, `\r\n` counts as one unit, which is "1 character big". Your second par doesn't make sense. You haven't even reached the newline, and yet you are saying it goes wrong - I suspect you meant to show something else?
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      1. USMats Petersson
 

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