Is it possible to define/scramble indeterminate values in C/C++ for debug purposes?

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Uninitialized variables may have indeterminate values, as this answer to an earlier question points out. Is there a way to specify this indeterminate data to, say, repeat 0xDEADDEAD? The indeterminate data is apparently compiler-specific, but it would always be nice to force it to be something easily recognizable.

Are there existing memory leak/corruption detection libraries allowing this? Overloading new seems like a solution in some cases, but I'd rather not delve into that trickery myself.

The problem is that indeterminate values usually cause undefined behaviour of code, and rarely occurring run time bugs, so, for example, I'd like to spot if I've forgotten a memset() somewhere in my code. Maybe even randomizing the indeterminate values could serve as a test bench.

In case this is not possible, are there better approaches to solve the problem?

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asked on Stack Overflow Jun 2, 2012 by phero • edited May 23, 2017 by Community

3 Answers

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Here are some guidelines for producing good quality C code:

  1. Create/use coding guidelines that help avoid memory bugs (and other types of bugs). There are many examples on the internet. The best approach is to take a look at 5 or 6 and compile it into one, keeping just the things that fit your needs.
  2. Use code reviews/inspections to find bugs and to check adherence to the coding guidelines. Code reviews is one of the best ways to find bugs that are undetectable by tools. Code reviews is extra important for beginner/intermiediate programmers, because it adds to your learning curve, both when you review code that others have written and when you are being reviewed.
  3. Test your code with test cases that can be run automatically.
  4. Use tools like valgrind to find many types of bugs.
answered on Stack Overflow Jun 2, 2012 by Klas Lindbäck
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To check the pattern of the value of the variables at runtime is a little bit tricky. As you say, it is compiler/architecture dependent.

Usually static analysis tools can give you warnings about uninitialized variables. Here's a free static code checker that you can play with: cppcheck.

answered on Stack Overflow Jun 2, 2012 by Alexandru C.
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There's indeterminate values, there are memory management errors, and there's the intersection of the two.

I don't know what, if anything C/C++ compilers do for indeterminate values. (A compiler I built for an arguably C like parallel language has an explicit debug switch, that fills every unassigned variable with a value designed to "cause trouble", e.g., for ints, -2^31, for pointers, specific not-void values gauranteed to cause a memory access fault, etc.). I suspect your mileage will vary here by compiler.

Memory management is notoriously hard. In C++ you can use constructors and destructors in a regular way to ensure that many of such errors don't occur, see stackoverflow.com/questions/76796/memory-management-in-c

C is harder, carefully inspecting your code, and ensuring each routine has clear responsibility for either allocation, deallocation or neither will help.

For both C and C++ you can use static analysis tools (Coverity, Fortify) to detect many such allocation errors. Similarly, you can use dynamic analysis tools such as Valgrind, which watches what your object code does and stops it when some memory management errors occur. For C only, you can use our dynamic analysis CheckPointer tool; it will detect all the errors valgrind detects and more (e.g., valgrind can't detect an access outside of a local array [one allocated in your stack]; CheckPointer can).

answered on Stack Overflow Jun 2, 2012 by Ira Baxter

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