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copied!<p>There's a lot here already, so maybe this is just a minor addition but here's what I find to be the biggest differences.</p> <p>Library:</p> <ul> <li>I put this first, because this in my opinion this is the biggest difference in practice. The C standard library is very(!) sparse. It offers a bare minimum of services. For everything else you have to roll your own or find a library to use (and many people do). You have file I/O and some very basic string functions and math. For everything else you have to roll your own or find a library to use. I find I miss extended containers (especially maps) heavily when moving from C++ to C, but there are a lot of other ones.</li> </ul> <p>Idioms:</p> <ul> <li>Both languages have manual memory (resource) management, but C++ gives you some tools to hide the need. In C you will find yourself tracking resources by hand much more often, and you have to get used to that. Particular examples are arrays and strings (C++ <code>vector</code> and <code>string</code> save you a lot of work), smart pointers (you can't really do "smart pointers" as such in C. You <em>can</em> do reference counting, but you have to up and down the reference counts yourself, which is very error prone -- the reason smart pointers were added to C++ in the first place), and the lack of RAII generally which you will notice everywhere if you are used to the modern style of C++ programming. <ul> <li>You have to be explicit about construction and destruction. You can argue about the merits of flaws of this, but there's a lot more explicit code as a result.</li> </ul></li> <li>Error handling. C++ exceptions can be tricky to get right so not everyone uses them, but if you do use them you will find you have to pay a lot of attention to how you do error notification. Needing to check for return values on all important calls (some would argue <em>all</em> calls) takes a lot of discipline and a lot of C code out there doesn't do it.</li> <li>Strings (and arrays in general) don't carry their sizes around. You have to pass a lot of extra parameters in C to deal with this.</li> <li>Without namespaces you have to manage your global namespace carefully. <ul> <li>There's no explicit tying of functions to types as there is with <code>class</code> in C++. You have to maintain a convention of prefixing everything you want associated with a type.</li> </ul></li> <li>You will see a lot more macros. Macros are used in C in many places where C++ has language features to do the same, especially symbolic constants (C has <code>enum</code> but lots of older code uses <code>#define</code> instead), and for generics (where C++ uses templates).</li> </ul> <p>Advice:</p> <ul> <li>Consider finding an extended library for general use. Take a look at <a href="http://library.gnome.org/devel/glib/stable/" rel="noreferrer">GLib</a> or <a href="http://apr.apache.org/" rel="noreferrer">APR</a>. <ul> <li>Even if you don't want a full library consider finding a map / dictionary / hashtable for general use. Also consider bundling up a bare bones "string" type that contains a size.</li> </ul></li> <li>Get used to putting module or "class" prefixes on all public names. This is a little tedious but it will save you a lot of headaches.</li> <li><p>Make heavy use of forward declaration to make types opaque. Where in C++ you might have private data in a header and rely on <code>private</code> is preventing access, in C you want to push implementation details into the source files as much as possible. (You actually want to do this in C++ too in my opinion, but C makes it easier, so more people do it.)</p> <p>C++ reveals the implementation in the header, even though it technically hides it from access outside the class.</p> <pre><code>// C.hh class C { public: void method1(); int method2(); private: int value1; char * value2; }; </code></pre> <p>C pushes the 'class' definition into the source file. The header is all forward declarations.</p> <pre><code>// C.h typedef struct C C; // forward declaration void c_method1(C *); int c_method2(C *); // C.c struct C { int value1; char * value2; }; </code></pre></li> </ul>

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