Are String Literals with the Same Content Guaranteed to Have the Same Address in Different Translation Units?

String Literal Address Consistency Across Translation Units

Question:

Is it reliable to assume that string literals with the same content will have the same memory address across different translation units (e.g., different source files)?

Answer:

No, relying on string literal addresses to be consistent across translation units is not portable and is considered unspecified behavior.

The C and C standards state that it is implementation-defined whether or not string literals with the same content will occupy distinct memory locations. This means that different compilers or runtime environments may handle string literals differently, potentially assigning them varying memory addresses.

Implications:

• If you attempt to assert that two string literals with the same content will have the same address across translation units, the assertion may fail on some compilers or platforms.
• Code that relies on string literal addresses for comparisons or other operations may exhibit unpredictable behavior.

Options:

If you require consistent string literal addresses within the same translation unit (i.e., a single source file), some compilers provide options like:

• GCC: -fmerge-constants to merge identical constants, including string literals.
• Visual Studio: /GF to enable string literal pooling.

Note:

• String literal address consistency across translation units is not guaranteed and should not be relied upon.
• If cross-unit string literal consistency is crucial, consider using a shared header file or passing string values explicitly between translation units.

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