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Every program shall contain exactly one definition of every non-inline function or object that is used in that program; no diagnostic required.

Wiki MarkupAlthough it is possible to check that the ODR is complied with (see \[ [Quinlan 06|AA. Bibliography#Quinlan 06]\]), as of October 2006 we are not aware of any compilers that fully enforce the rule or even issue a diagnostic. The EDG [C++ Front End|https://www.edg.com/index.php?location=c_frontend] diagnoses a subset of violations of the ODR when compiling in export mode (a mode where the C++ {{export}} feature is enabled). As the paper by Quinlan et al. shows, failing to enforce the ODR enables a virtual function pointer attack, known as the VPTR [exploit|BB. Definitions#exploit]. This is where an object's virtual function table is corrupted so that calling a virtual function on the object results in malicious code being executed. See the paper by Quinlan et al. for more details.

Non-Compliant Code Example

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Bibliography

Wiki Markup\[[ISO/IEC 14882-2003|AA. Bibliography#ISO/IEC 14882-2003]\] Section 3.2, "One definition rule"

Wiki Markup\[[Quinlan 06|AA. Bibliography#Quinlan 06]\]

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MSC32-CPP. Ensure your random number generator is properly seeded      49. Miscellaneous (MSC)      MSC34-CPP. Do not modify the standard namespace