Why are `long int`, `int64_t`, and `long long int` Not Always Equivalent in C ?

Compiler Confusion: Understanding the Difference Between long int, int64_t, and long long int

Introduction

Type traits in C offer powerful functionality, but can sometimes lead to unexpected behavior. One such scenario involves the potential differences between long int, int64_t, and long long int.

Problem

As highlighted in the given code sample, the behavior of type traits handling these types varies depending on the compilation architecture (32-bit vs. 64-bit). This issue stems from the underlying definition of int64_t, which changes based on the word size.

Solution

While it may seem logical to expect these types to be equivalent, recognizing their fundamental differences is crucial. Due to the way C/C defines basic data types, explicitly defining type equivalence is impossible, as it could potentially disrupt the language.

Workaround

Instead of seeking an equivalence solution, the correct approach is to design type traits that rely on the properties of the type rather than its exact identifier. By utilizing techniques like disabling overloads based on specific conditions or leveraging C 11's standard disable_if syntax, developers can handle these types effectively without creating duplicate code.

Conclusion

Understanding the inherent differences between these types and employing the appropriate workaround strategies ensures the reliability and maintainability of C code.

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