Here’s my attempt at an interpretation: The standard simply says you mustn’t do this, even though any given concrete implementation may have no problem supporting such a construction. But imagine for example if someone wanted to write a “small vector” optimization by which a vector always contains space for, say, five elements. Immediately you’d be … Read more
Because the size of a vector is an unsigned integral type. You are comparing an unsigned type with a signed one, and the two’s complement negative signed integer is being promoted to unsigned. That corresponds to a large unsigned value. This code sample shows the same behaviour that you are seeing: #include <iostream> int main() … Read more
When you call srand(x), then the value of x determines the sequence of pseudo-random numbers returned in following calls to rand(), depending entirely on the value of x. When you’re in a loop and call srand() at the top: while (…) { srand(time(0)); x = rand(); y = rand(); } then the same random number … Read more
The current C++ standard does not require that compilers support VLAs. However, compiler vendors are permitted to support VLAs as an extension. GCC >= 4.7, for example, does. It was originally proposed that VLAs would appear in C++14, however the proposal did not succeed. They also, ultimately, did not appear in C++17.
I am using openssl 0.9.6g and I have created public/private keypair using RSA_generate_key(). It gives me keys like: —–BEGIN RSA PUBLIC KEY—– … —–END RSA PUBLIC KEY—– I think what I am looking for is “how to convert rsa public key from pkcs#1 to x509 format. Yeah, .Net can consume some ASN.1/DER encoded keys, and … Read more
You get 1 because regex_search returns only 1 match, and size() will return the number of capture groups + the whole match value. Your matches is…: Object of a match_results type (such as cmatch or smatch) that is filled by this function with information about the match results and any submatches found. If [the regex … Read more
That’s because pointers don’t behave like integers. It’s undefined behavior because the standard says so. On most platforms however (if not all), you won’t get a crash or run into dubious behavior if you don’t dereference the array. But then, if you don’t dereference it, what’s the point of doing the addition? That said, note … Read more
Since yours is now the third “How do I build boost on Windows?” question that I’ve seen since 1.60.0 was released here are my own personal Windows boost build notes: Windows does not directly support boost, so you can download it and put it wherever you want. The boost user guide recommends creating a BOOST_ROOT … Read more
The C++ Standard(2003) says in ยง5.6/4, […] If the second operand of / or % is zero the behavior is undefined; […] That is, following expressions invoke undefined-behavior(UB): X / 0; //UB X % 0; //UB Note also that -5 % 2 is NOT equal to -(5 % 2) (as Petar seems to suggest in … Read more
You can not rely on identical string literals having the same memory location, it is an implementation decision. The C99 draft standard tells us that it is unspecified whether the same string literal are distinct, from section 6.4.5 String literals: It is unspecified whether these arrays are distinct provided their elements have the appropriate values. … Read more