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POReading a text file backwards in C
 

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  1. POReading a text file backwards in C
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    <p>What's the best way to read a file backwards in C? I know at first you may be thinking that this is no use whatsoever, but most logs etc. append the most recent data at the end of the file. I want to read in text from the file backwards, buffering it into lines - that is</p> <p>abc<br> def<br> ghi</p> <p>should read <b>ghi</b>, <b>def</b>, <b>abc</b> in lines.</p> <p>So far I have tried:</p> <pre><code> #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; void read_file(FILE *fileptr) { char currentchar = '\0'; int size = 0; while( currentchar != '\n' ) { currentchar = fgetc(fileptr); printf("%c\n", currentchar); fseek(fileptr, -2, SEEK_CUR); if( currentchar == '\n') { fseek(fileptr, -2, SEEK_CUR); break; } else size++; } char buffer[size]; fread(buffer, 1, size, fileptr); printf("Length: %d chars\n", size); printf("Buffer: %s\n", buffer); } int main(int argc, char *argv[]) { if( argc &lt; 2) { printf("Usage: backwards [filename]\n"); return 1; } FILE *fileptr = fopen(argv[1], "rb"); if( fileptr == NULL ) { perror("Error:"); return 1; } fseek(fileptr, -1, SEEK_END); /* Seek to END of the file just before EOF */ read_file(fileptr); return 0; } </code></pre> <p>In an attempt to simply read one line and buffer it. Sorry that my code is terrible, I am getting so very confused. I know that you would normally allocate memory for the whole file and then read in the data, but for large files that constantly change I thought it would be better to read directly (especially if I want to search for text in a file).</p> <p>Thanks in advance</p> <p><strong>* Sorry forgot to mention this will be used on Linux, so newlines are just NL without CR. *</strong></p>
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    1. COYou could possibly [memory map the file](http://en.wikipedia.org/wiki/Memory-mapped_file), and use pointer arithmetic to "read" the file. Might be simpler than having to constantly jump around with the file pointer.
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    2. COFrom the C standard: `A binary stream need not meaningfully support fseek calls with a whence value of SEEK_END.`
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    3. COProbably you could log into DB instead of plain file?
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