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  1. #include <iostream>
  2. #include <string>
  3.  
  4. // minimap example-class to test
  5. // - constructor variable shadowing
  6. // - assigning to const-refs -- see https://stackoverflow.com/questions/27423364/binding-const-of-temporary-no-compiler-warning
  7.  
  8. // the device-under-test:
  9. class TestClass {
  10.   public:
  11.     std::string a;
  12.     std::string b;
  13.     const std::string &c;
  14.     // removing the "reference" whould remove the temporary-problem
  15.     const std::string &d;
  16.  
  17.     TestClass(std::string a, std::string b, const std::string &c,
  18.               const std::string &d)
  19.         : a(a), b(b), c(c), d(d) {
  20.         // pitfall: changing the variable "a" from the constructor-call, not
  21.         // the actual member variable
  22.         a = "A";
  23.         // using pointer-indirection the lookup-semantics are different and the
  24.         // member variable is found instead
  25.         this->b = "B";
  26.         // "c" is a const-ref, cannot be changed at all... if it is assigned some
  27.         // temporary value it is mangled up...
  28.     }
  29. };
  30.  
  31. int main() {
  32.  
  33.     // a stack-resident variable, where we can safely pass a const-ref
  34.     std::string c("c");
  35.     // creating the actual test-oject.
  36.     //
  37.     // NOTE: the fourth variable "d" is a
  38.     // temporary, whose reference is not valid... what I don't get in the
  39.     // moment: why does no compiler warn me?
  40.     TestClass dut("a", "b", c, "d");
  41.  
  42.     // and printing what we got:
  43.     std::cout << "beginning output:\n\n";
  44.     std::cout << "dut.a: '" << dut.a << "'\n";
  45.     std::cout << "dut.b: '" << dut.b << "'\n";
  46.     std::cout << "dut.c: '" << dut.c << "'\n";
  47.     // this will abort the program (gcc-4.9.1) or be an empty string
  48.     // (clang-3.5) -- don't know whats going on here... I mean I know why
  49.     // it should segfault (using reference of temporary), but why does no
  50.     // compiler warn here?
  51.     //std::cout << "dut.d: '" << dut.d << "'\n";
  52.     std::cout << "\nthats it!\n";
  53.  
  54.     return 0;
  55. }
Success #stdin #stdout 0s 3472KB
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stdin
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Standard input is empty
stdout
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beginning output:

dut.a: 'a'
dut.b: 'B'
dut.c: 'c'

thats it!
https://ideone.com/NDI9Gw
language:
C++ (gcc 8.3)
created:
10 years ago
visibility:
public

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