I Do Not Know C: Short quiz on undefined behavior (2015)
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Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#2Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#3IMHO the problem is with compilers (and their developers) who think UB really means they can do anything, when what programmers usually expect is, and the standard even notes for one of the possible interpretations of UB, "behaving during translation or program execution in a documented manner characteristic of the environment".
Related reading:
http://blog.metaobject.com/2014/04/cc-osmartass.html
http://blog.regehr.org/archives/1180 and https://news.ycombinator.com/item?id=8233484
Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#41. Unless C's variable definition rules are completely different from C++'s, int i; is a full definition, not a declaration. If both definitions appear at the same scope (e.g. global), this will cause either a compiler error or a linker error. A variable declaration would be extern int i;
Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#5I suppose this sort of ambiguity is what drives the passion of Rust and Go programmers.
Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#61. Unless C's variable definition rules are completely different from C++'s, int i; is a full definition, not a declaration. If both definitions appear at the same scope (e.g. global), this will cause either a compiler error or a linker error. A variable declaration would be extern int i;
C's variable definition rules are different from C++'s. gcc happily compiles those two lines, g++ exits with the "redefinition" error.
Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#7IMHO the problem is with compilers (and their developers) who think UB really means they can do anything , when what programmers usually expect is, and the standard even notes for one of the possible interpretations of UB, "behaving during translation or program execution in a documented manner characteristic of the environment". Related reading: http://blog.metaobject.com/2014/04/cc-osmartass.html http://blog.regehr…
There's no compiler writers throwing out
if(undefined_behavior) {
ruin_developers_day();
}
Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#8It's worth noting that for example #12, the assert will only fire for debug builds (i.e. the macro NDEBUG is not defined). So, depending on how the source is compiled, it may be able to invoke the div function with b == 0.
Re: I Do Not Know C: Short quiz on undefined behavior (2015)
#91. Unless C's variable definition rules are completely different from C++'s, int i; is a full definition, not a declaration. If both definitions appear at the same scope (e.g. global), this will cause either a compiler error or a linker error. A variable declaration would be extern int i;
C's variable definition rules are different from C++'s. gcc happily compiles those two lines, g++ exits with the "redefinition" error.
That was unexpected.