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    <pre><code>#include &lt;stdio.h&gt; static void cat(FILE *fp) { char buffer[4096]; size_t nbytes; while ((nbytes = fread(buffer, sizeof(char), sizeof(buffer), fp)) != 0) fwrite(buffer, sizeof(char), nbytes, stdout); } int main(int argc, char **argv) { FILE *fp; const char *file; while ((file = *++argv) != 0) { if ((fp = fopen(file, "r")) != 0) { cat(fp); fclose(fp); } } return(0); } </code></pre> <p>The <code>cat()</code> function is not strictly necessary, but I'd rather use it. The main program steps through each command line argument and opens the named file. If it succeeds, it calls the <code>cat()</code> function to print its contents. Since the call to <code>fopen()</code> does not specify <code>"rb"</code>, it is opened as a text file. If the file is not opened, this code silently ignores the issue. If no files are specified, nothing is printed at all.</p> <p>The <code>cat()</code> function simply reads blocks of text up to 4096 bytes at a time, and writes them to standard output ('the screen'). It stops when there's no more to read.</p> <p>If you want to extend the code to read standard input when no file is specified, then you can use:</p> <pre><code>if (argc == 1) cat(stdin); else { ...while loop as now... } </code></pre> <p>which is one of the reasons for having the <code>cat()</code> function written as shown.</p> <p>This code does not pay direct attention to newlines — or lines of any sort. If you want to process it formally one line at a time, then you can do several things:</p> <pre><code>static void cat(FILE *fp) { char buffer[4096]; while (fgets(buffer, sizeof(buffer), fp) != 0) fputs(buffer, stdout); } </code></pre> <p>This will read and write one line at a time. If any line is longer than 4095 bytes, it will read the line in two or more operations and write it in the same number of operations. Note that this assumes a text file in a way that the version using <code>fread()</code> and <code>fwrite()</code> does not. On POSIX systems, the version with <code>fread()</code> and <code>fwrite()</code> will handle arbitrary binary files with null bytes (<code>'\0'</code>) in the data, but the version using <code>fgets()</code> and <code>fputs()</code> will not. Both the versions so far are strictly standard C (any version of the standard) as they don't use any platform-specific extensions; they are about as portable as code can be.</p> <p>Alternatively again, if you have the POSIX 2008 <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/getline.html" rel="nofollow"><code>getline()</code></a> function, you can use that, but you need <code>#include &lt;stdlib.h&gt;</code> too (because you end up having to release the memory it allocates):</p> <pre><code>static void cat(FILE *fp) { char *buffer = 0; size_t buflen = 0; while (getline(&amp;buffer, &amp;buflen, fp) != -1) fputs(buffer, stdout); free(buffer); } </code></pre> <p>This version, too, will not handle binary data (meaning data with null bytes in it). It could be upgraded to do so, of course:</p> <pre><code>static void cat(FILE *fp) { char *buffer = 0; size_t buflen = 0; ssize_t nbytes; while ((nbytes = getline(&amp;buffer, &amp;buflen, fp)) != -1) fwrite(buffer, sizeof(char), nbytes, stdout); free(buffer); } </code></pre> <p>The <code>getline()</code> function reports how many bytes it read (there's a null byte after that), but the <code>fwrite()</code> function is the only one that takes a stream of arbitrary bytes and writes them all to the given stream.</p>
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    1. POClearest way to read and print .txt file lines in C
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    1. USJonathan Leffler
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    1. COWhy the fixed size buffer? A malloc wouldn't be hard with a stat call, and much more secure and portable, not to mention better.
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      1. USLinuxios
    2. COMore secure ? More portable ? Why ? Slower yes, remember that everything on the stack is most likely in the CPU cache... Why using the HEAP (a malloc is not slow, but it is not fast) ?
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    3. COa malloc() would cause extra conditions. Also: the program is I/O bound anyway, and read_bunch + write_bunch is disastrous for the disk-LRU.
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      1. USwildplasser
 

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