How to verify if a void pointer (void *) is one of two data types?

by

The translation of void* is
“Dear compiler, this is a pointer, an there is no additional information for you on this.”.

Usually the compiler knows better than you (the programmer), because of information he got earlier and still remembers and you might have forgotten about.
But in this special case, you know better or need to know better. In all cases of void* the information is available otherwise, but only to the programmer, who “happens to know”. The programmer therefor has to provide the information to the compiler – or better to the running program, because the one advantage a void* has is that the information can change during runtime.
Usually that is done by giving the information via additional parameters to functions, sometimes via context, i.e. the program “happens to know” (e.g. for each possible type there is a separate function, whichever function gets called implies the type).

So in the end void* does not contain the type info.
Many programmers misunderstand this as “I don’t need to know the type info”.
But the opposite is true, the use of void* increases the responsibility of the programmer to keep track of the type info and provide it appropriatly to the program/compiler.

More Related Contents:

  1. Should C compilers immediately free "further unused" memories? [closed]
  2. How can I indicate that the memory *pointed* to by an inline ASM argument may be used?
  3. Where is PATH_MAX defined in Linux?
  4. Fused multiply add and default rounding modes
  5. Status of __STDC_IEC_559__ with modern C compilers
  6. Equivalents to MSVC’s _countof in other compilers?
  7. Is free() zeroing out memory?
  8. Why both clang and gcc only give a warning when there is a space after backslash if C standard says that whitespace is forbidden?
  9. Is char signed or unsigned by default?
  10. Modulo operation with negative numbers
  11. C undefined behavior. Strict aliasing rule, or incorrect alignment? [duplicate]
  12. Are all data pointers the same size in one platform for all data types? [duplicate]
  13. Where in memory are my variables stored in C?
  14. Order of local variable allocation on the stack
  15. What is the meaning of lines starting with a hash sign and number like ‘# 1 “a.c”‘ in the gcc preprocessor output?
  16. Undefined reference to `pow’ and `floor’
  17. Adding leading underscores to assembly symbols with GCC on Win32?
  18. How to include needed C library using gcc?
  19. Creating static Mac OS X C build
  20. Why does gcc allow arguments to be passed to a function defined to be with no arguments?
  21. Why we need Clobbered registers list in Inline Assembly?
  22. What is “…” in switch-case in C code
  23. How to link to a different libc file?
  24. C code with undefined results, compiler generates invalid code (with -O3)
  25. /usr/bin/ld: cannot find -lc while compiling with makefile
  26. How to compile and run C in sublime text 3?
  27. C11 in GCC?
  28. Produce loops without cmp instruction in GCC
  29. Using condition flags as GNU C inline asm outputs
  30. What exactly is -fno-builtin doing here?

Leave a Comment