What Breaking Changes Should I Be Aware Of When Migrating Code to C 11?

Breaking Changes in C 11

C 11 introduced significant changes that may impact the compilation of existing code, including the following:

Core Language

• The introduction of explicit operator bool() in the standard library, replacing instances of operator void*(). This change may cause code that previously relied on implicit conversions to fail to compile.
• New keywords, including alignas, alignof, char16_t, constexpr, and nullptr, may conflict with existing identifiers in code that did not follow naming conventions.
• The behavior of integer division has changed, as C 11 always rounds the result towards 0, while C 03 allowed for rounding towards 0 or negative infinity.
• Implicitly-declared special member functions, such as constructors or destructors, are now defined as deleted if their implicit definition would have been ill-formed, which may cause code using these functions in certain contexts to become invalid.
• User-declared destructors have an implicit exception specification, meaning they cannot throw exceptions. Code that relies on destructors throwing exceptions may need to be modified.
• Dependent calls of functions with internal linkage are now allowed, which may change the resolution of overloaded functions in templates.

Library Changes

• Identifiers added to the C standard library in C 11 may conflict with existing identifiers in code that used headers with the same names.
• The swap function has been moved from the header to the header. Code that includes may need to be updated to include instead.
• The global namespace posix is now reserved for standardization. Code that defines identifiers in this namespace may need to be modified.
• Macros named override, final, carries_dependency, or noreturn are invalid in C 11. Code that defines these macros may need to be updated.

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