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copied!<p>In both cases, the cast is unnecessary and can mask errors; I'll delete the casts in the following. (<code>malloc()</code> returns a <code>void*</code>, which can be implicitly converted to a pointer-to-whatever.)</p> <pre><code>char **args = malloc(MAX_ARGS*sizeof(char*)); </code></pre> <p>This defined <code>args</code> as a pointer-to-pointer-to-char, and initializes it to point to a chunk of memory big enough to hold <code>MAX_ARGS</code> elements, each of which is a <code>char*</code>. Once you've done this, you'll want to assign values to those <code>char*</code> elements, likely making them point to strings.</p> <pre><code>char *args = malloc(MAX_ARGS*sizeof(char*)); </code></pre> <p>This is <em>legal</em>, but almost certainly a logical error. <code>args</code> is a pointer-to-char, which means it can point either to a single <code>char</code> object, or to the first element of an array of <code>char</code> elements. But you're allocating memory that can hold <code>MAX_ARGS</code> <em>pointers</em>.</p> <p>A more likely thing to do is:</p> <pre><code>char *s = malloc(MAX_LEN); </code></pre> <p>which will cause <code>s</code> to point to a region of memory that can hold <code>MAX_LEN</code> <code>char</code> elements (a string of length up to <code>MAX_LEN - 1</code>). (Note that <code>sizeof (char) == 1</code> by definition.)</p> <p>There's a useful trick to avoid type mismatches. A pointer of type <code>FOO*</code>, for any type <code>FOO</code>, needs to point to a chunk of memory big enough to old one or more elements of type <code>FOO</code>. If you write:</p> <pre><code>ptr = malloc(count * sizeof *ptr); </code></pre> <p>and <code>ptr</code> is a <code>FOO*</code>, then <code>sizeof *ptr</code> is the same as <code>sizeof (FOO)</code> -- but you won't have to update the line if you later change <code>ptr</code> to be a <code>pointer to</code>BAR`.</p> <p>In your case, the pointed-to type is itself a pointer, so you can write:</p> <pre><code>char **args = malloc(MAX_ARGS * sizeof *args); </code></pre> <p>And when you call <code>malloc</code>, you should <em>always</em> check whether it succeeded, and take some action if it failed -- even if that action is to terminate the program with an error message:</p> <pre><code>if (args == NULL) { fprintf(stderr, "malloc failed\n"); exit(EXIT_FAILURE); } </code></pre>

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