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问题 I know that EOF and '\0' are of type integers, but if so shouldn't they have a fixed value? I printed both and got -1 for EOF and 0 for '\0' . But are these values fixed? I also had this int a=-1; printf("%d",a==EOF); //printed 1 Are the value for EOF and '\0' fixed integers? 回答1: EOF is a macro which expands to an integer constant expression with type int and an implementation dependent negative value but is very commonly -1. '\0' is a char with value 0 in C++ and an int with the value 0 in

问题 I know that EOF and '\0' are of type integers, but if so shouldn't they have a fixed value? I printed both and got -1 for EOF and 0 for '\0' . But are these values fixed? I also had this int a=-1; printf("%d",a==EOF); //printed 1 Are the value for EOF and '\0' fixed integers? 回答1: EOF is a macro which expands to an integer constant expression with type int and an implementation dependent negative value but is very commonly -1. '\0' is a char with value 0 in C++ and an int with the value 0 in

问题 Apparently PostgreSQL stores a couple of values in the header of each database row. If I don't use NULL values in that table - is the null bitmap still there? Does defining the columns with NOT NULL make any difference? 回答1: It's actually more complex than that. The null bitmap needs one bit per column in the row, rounded up to full bytes. It is only there if the actual row includes at least one NULL value and is fully allocated in that case. NOT NULL constraints do not directly affect that.

问题 Is it safe to assume that NULL always translates to false in C? void *somePtr = NULL; if (!somePtr) { /* This will always be executed? */ } Or should an explicit check against the value of NULL be made? 回答1: Yes. NULL evaluates to false, since C considers any non-zero value true and any zero value false. NULL is essentially the zero address and is treated as such in comparisons, and I believe would be promoted to an int for the boolean check. I would expect that your code is readable to

问题 Is null an Object in Java? 回答1: If null were an Object, it would support the methods of java.lang.Object such as equals() . However, this is not the case - any method invocation on a null results in a NullPointerException . And this is what the Java Language Specification has to say on this topic: There is also a special null type, the type of the expression null, which has no name. Because the null type has no name, it is impossible to declare a variable of the null type or to cast to the

问题 Is it safe to check a pointer to not being NULL by writing simply if(pointer) or do I have to use if(pointer != NULL) ? 回答1: You can; the null pointer is implicitly converted into boolean false while non-null pointers are converted into true. From the C++11 standard, section on Boolean Conversions: A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a prvalue of type bool . A zero value, null pointer value, or null member pointer value is

问题 Every so often when programmers are complaining about null errors/exceptions someone asks what we do without null. I have some basic idea of the coolness of option types, but I don't have the knowledge or languages skill to best express it. What is a great explanation of the following written in a way approachable to the average programmer that we could point that person towards? The undesirability of having references/pointers be nullable by default How option types work including strategies

问题 Every so often when programmers are complaining about null errors/exceptions someone asks what we do without null. I have some basic idea of the coolness of option types, but I don't have the knowledge or languages skill to best express it. What is a great explanation of the following written in a way approachable to the average programmer that we could point that person towards? The undesirability of having references/pointers be nullable by default How option types work including strategies

问题 This question already has answers here : How to avoid NoMethodError for missing elements in nested hashes, without repeated nil checks? (17 answers) Closed 3 years ago . I'm interested in getting the nested 'name' parameter of a params hash. Calling something like params[:subject][:name] throws an error when params[:subject] is empty. To avoid this error I usually write something like this: if params[:subject] && params[:subject][:name] Is there a cleaner way to implement this? 回答1: Check Ick

问题 Will null instanceof SomeClass return false or throw a NullPointerException ? 回答1: No, a null check is not needed before using instanceof. The expression x instanceof SomeClass is false if x is null . From the Java Language Specification, section 15.20.2, "Type comparison operator instanceof": "At run time, the result of the instanceof operator is true if the value of the RelationalExpression is not null and the reference could be cast to the ReferenceType without raising a ClassCastException