implementation-defined-behavior

问题 I posted a question with my code whose only #include directive was the following: #include <bits/stdc++.h> My teacher told me to do this, but in the comments section I was informed that I shouldn't. Why? 回答1: Including <bits/stdc++.h> appears to be an increasingly common thing to see on Stack Overflow, perhaps something newly added to a national curriculum in the current academic year. I imagine the advantages are vaguely given thus: You only need write one #include line You do not need to

问题 Here's a simple function that tries to do read a generic twos-complement integer from a big-endian buffer, where we'll assume std::is_signed_v<INT_T> : template<typename INT_T> INT_T read_big_endian(uint8_t const *data) { INT_T result = 0; for (size_t i = 0; i < sizeof(INT_T); i++) { result <<= 8; result |= *data; data++; } return result; } Unfortunately, this is undefined behaviour, as the last <<= shifts into the sign bit. So now we try the following: template<typename INT_T> INT_T read_big

问题 What is undefined behavior in C and C++? What about unspecified behavior and implementation-defined behavior? What is the difference between them? 回答1: Undefined behavior is one of those aspects of the C and C++ language that can be surprising to programmers coming from other languages (other languages try to hide it better). Basically, it is possible to write C++ programs that do not behave in a predictable way, even though many C++ compilers will not report any errors in the program! Let's

问题 I can\'t find an answer in the standard documentation. Does the C++ language standard require sizeof(bool) to always be 1 (for 1 byte), or is this size implementation-defined? 回答1: sizeof(bool) is implementation defined, and the standard puts notable emphasis on this fact. §5.3.3/1, abridged: sizeof(char) , sizeof(signed char) and sizeof(unsigned char) are 1; the result of sizeof applied to any other fundamental type is implementation-defined. [Note: in particular, sizeof(bool) and sizeof

问题 I posted a question with my code whose only #include directive was the following: #include <bits/stdc++.h> My teacher told me to do this, but in the comments section I was informed that I shouldn\'t. Why? 回答1: Including <bits/stdc++.h> appears to be an increasingly common thing to see on Stack Overflow, perhaps something newly added to a national curriculum in the current academic year. I imagine the advantages are vaguely given thus: You only need write one #include line You do not need to