StackOverflow2013

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POMake conversion to a native type explicit in C++
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copied!<p>I'm trying to write a class that implements 64-bit ints for a compiler that doesn't support <code>long long</code>, to be used in existing code. Basically, I should be able to have a typedef somewhere that selects whether I want to use <code>long long</code> or my class, and everything else should compile and work.</p> <p>So, I obviously need conversion constructors from <code>int</code>, <code>long</code>, etc., and the respective conversion operators (casts) to those types. This seems to cause errors with arithmetic operators. With native types, the compiler "knows" that when <code>operator*(int, char)</code> is called, it should promote the <code>char</code> to <code>int</code> and call <code>operator*(int, int)</code> (rather than casting the <code>int</code> to <code>char</code>, for example). In my case it gets confused between the various built-in operators and the ones I created.</p> <p>It seems to me like if I could flag the conversion operators as explicit somehow, that it would solve the issue, but as far as I can tell the <code>explicit</code> keyword is only for constructors (and I can't make constructors for built-in types).</p> <p>So is there any way of marking the casts as explicit? Or am I barking up the wrong tree here and there's another way of solving this? Or maybe I'm just doing something else wrong...</p> <p>EDIT:</p> <p>A little clarification on what I want to do: I have a project that uses 64-bit ('long long`) operations in many places, and I am trying to port it to a platform that <em>doesn't</em> have built-in support for 64-bit variables/operations. Even though I have the source for the project, I would really prefer not to have to go over the thousands of places where built-in operators and C-style casts are and change them around.</p> <p>As for the code itself, the project has the following definitions and kinds of code:</p> <pre><code>typedef long long i64; // I would like to only have to change this to use my class instead of "long long" int a; unsigned b; int c = ((i64)a*b)>>32; </code></pre> <p>As for the class implementation, I have the following:</p> <pre><code>class Long64 { public: Long64(); Long64(const Long64&); Long64(int); Long64(long); Long64(unsigned int); Long64(unsigned long); operator int() const; operator long() const; operator unsigned int() const; operator unsigned long() const; friend Long64 operator*(int l, const Long64& r); friend Long64 operator*(const Long64& l, int r); friend Long64 operator*(long l, const Long64& r); friend Long64 operator*(const Long64& l, long r); } </code></pre>

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