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POC: Nested Ifs or Gotos
 

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    <p>What is the best way to manage resources for a <strong>C</strong> program. Should I use a nested if structure or should I use goto statements? </p> <p>I am aware there is a lot of <strong>taboo</strong> about <strong>goto</strong> statements. However, I think it is justified for local resource clean up. I have supplied two samples. One compares a nested if structure and another uses goto statements. I personally find the goto statements make the code easier to read. For those who might argue that the <strong>nested if</strong> prompt better structure, imagine if the datatype was something other than a char*, like a Windows handle. I feel that the <strong>nested if</strong> structure would get out of hand with a series of <strong><a href="http://msdn.microsoft.com/en-us/library/aa363858(VS.85).aspx" rel="nofollow noreferrer">CreateFile</a></strong> functions or any other function that takes large quantities of parameters.</p> <p>This <a href="http://vilimpoc.org/research/raii-in-c/" rel="nofollow noreferrer">article</a> demonstrates that local goto statements create RAII for C code. The code is neat an easy to follow. Imagine that as a series of <strong>nested if</strong> statements. </p> <p>I understand that <strong>goto</strong> is taboo in many other languages because their exists other control mechanisms like try/catch etc, however, in C it seems appropriate.</p> <pre><code>#include &lt;stdlib.h&gt; #define STRING_MAX 10 void gotoExample() { char *string1, *string2, *string3, *string4, *string5; if ( !(string1 = (char*) calloc(STRING_MAX, sizeof(char))) ) goto gotoExample_string1; if ( !(string2 = (char*) calloc(STRING_MAX, sizeof(char))) ) goto gotoExample_string2; if ( !(string3 = (char*) calloc(STRING_MAX, sizeof(char))) ) goto gotoExample_string3; if ( !(string4 = (char*) calloc(STRING_MAX, sizeof(char))) ) goto gotoExample_string4; if ( !(string5 = (char*) calloc(STRING_MAX, sizeof(char))) ) goto gotoExample_string5; //important code goes here gotoExample_string5: free(string4); gotoExample_string4: free(string3); gotoExample_string3: free(string2); gotoExample_string2: free(string1); gotoExample_string1: } void nestedIfExample() { char *string1, *string2, *string3, *string4, *string5; if (string1 = (char*) calloc(STRING_MAX, sizeof(char))) { if (string2 = (char*) calloc(STRING_MAX, sizeof(char))) { if (string3 = (char*) calloc(STRING_MAX, sizeof(char))) { if (string4 = (char*) calloc(STRING_MAX, sizeof(char))) { if (string5 = (char*) calloc(STRING_MAX, sizeof(char))) { //important code here free(string5); } free(string4); } free(string3); } free(string2); } free(string1); } } int main(int argc, char* argv[]) { nestedIfExample(); gotoExample(); return 0; } </code></pre> <p>I would also like to quote Linus Torvalds on <strong>goto</strong> statements inside the Linux <a href="http://kerneltrap.org/node/553/2131" rel="nofollow noreferrer">Kernel</a>.</p> <blockquote> <p>And sometimes structure is <em>bad</em>, and gets into the way, and using a "goto" is just much clearer.</p> <p>For example, it is quite common to have conditionals THAT DO NOT NEST.</p> <p>In which case you have two possibilities</p> <ul> <li><p>use goto, and be happy, since it doesn't enforce nesting</p> <p>This makes the code <em>more</em> readable, since the code just does what the algorithm says it should do.</p></li> <li><p>duplicate the code, and rewrite it in a nesting form so that you can<br> use the structured jumps.</p> <p>This often makes the code much LESS readable, harder to maintain, and bigger.</p></li> </ul> <p>The Pascal language is a prime example of the latter problem. Because it doesn't have a "break" statement, loops in (traditional) Pascal end up often looking like total shit, because you have to add totally arbitrary logic to say "I'm done now".</p> </blockquote> <p>Is <strong>goto</strong> acceptable for resource management? Should I use <strong>nested if</strong> statements or is there a better way?</p> <p><strong>Update:</strong> <a href="https://stackoverflow.com/questions/245742/examples-of-good-gotos-in-c-or-c">Examples of Good Gotos In C</a></p>
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    1. COnote that your goto's goto the wrong place -- if your malloc for string1 fails, you don't want to free the memory you couldn't allocate :)
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    2. CO@KevinDTimm: A failed allocation is signaled by a null pointer -- and passing a null pointer to `free` is harmless (a nop). In this case, assuring you `free` only the successful allocations leads to (considerable) extra work.
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    3. CO@Jerry - while that is true, it's a tough paradigm for many to grok. The freeing of a null pointer can be a task switch and so I try not to do it (therefore, only freeing successful allocations)
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