c11 | 易学教程

Does any C library implement C11 threads for GNU/Linux?

阅读更多关于 Does any C library implement C11 threads for GNU/Linux?

问题 There have been a lot of questions about C11 and C11 threading, but I don\'t see a definitive answer anywhere: Does any C library implement the C11 threading interface usable on GNU/Linux-like? e.g., provide the \"optional\" <threads.h> and the thread support library like thrd_create() , from the C11 standard near p. 376. Ideally, I\'d like to find a library that is common-ish, open-source or free, for common/generic/multi architecture (e.g., GNU/Linux, x86_64, or portable-ish). A few of the

C11 GCC threads.h not found?

阅读更多关于 C11 GCC threads.h not found?

问题 The following code #include <threads.h> Gives me this error: fatal error: threads.h: No such file or directory Using the latest GCC and Clang with -std=c11. Is C11 threading not supported by GCC and Clang? Or is there a hack (or something to install) to get it? I\'m just using Ubuntu 14.04 with the gcc and clang packages from the Ubuntu repo. 回答1: The gcc document C11 status indicates that it does not support threading, it says: Threading [Optional] | Library issue (not implemented) As the

What are anonymous structs and unions useful for in C11?

阅读更多关于 What are anonymous structs and unions useful for in C11?

C11 adds, among other things, 'Anonymous Structs and Unions'. I poked around but could not find a clear explanation of when anonymous structs and unions would be useful. I ask because I don't completely understand what they are. I get that they are structs or unions without the name afterwards, but I have always (had to?) treat that as an error so I can only conceive a use for named structs. Anonymous union inside structures are very useful in practice. Consider that you want to implement a discriminated sum type (or tagged union ), an aggregate with a boolean and either a float or a char* (i

Reading a character with scanf_s

阅读更多关于 Reading a character with scanf_s

问题 I was just messing around with C and ran into this small problem. As you can see from my output I getting \'╠\' this character. #include <stdio.h> int main(void) { char c; printf(\"Do you want to be X\'s or O\'s?\\n\"); scanf_s(\"%c\", &c); printf(\"You chose %c\\n\", c); } See program output 回答1: You are misusing scanf_s() . Microsoft compilers may warn you to use their secure extensions (aka c11 annex k). But, be careful if you do so. scanf_s() is not a direct replacement for scanf() . In

Operator precedence table for the C programming language

阅读更多关于 Operator precedence table for the C programming language

问题 What would a correct operator precedence table that lists all operators in the C language look like? I have made extensive searches on the web, and found many such precedence tables. Alas, I haven\'t found a single one filling these requirements: Lists all operators in the C language as defined in ISO 9899:2011, without mixing in any C++ operators. Lists the operators in the complete and correct priority order. 回答1: Explanation Prec. denotes operator precedence , where group 1 has the highest

Does &((struct name *)NULL -> b) cause undefined behaviour in C11?

阅读更多关于 Does &((struct name *)NULL -> b) cause undefined behaviour in C11?

问题 Code sample: struct name { int a, b; }; int main() { &(((struct name *)NULL)->b); } Does this cause undefined behaviour? We could debate whether it \"dereferences null\", however C11 doesn\'t define the term \"dereference\". 6.5.3.2/4 clearly says that using * on a null pointer causes undefined behaviour; however it doesn\'t say the same for -> and also it does not define a -> b as being (*a).b ; it has separate definitions for each operator. The semantics of -> in 6.5.2.3/4 says: A postfix

Syntax and Sample Usage of _Generic in C11

阅读更多关于 Syntax and Sample Usage of _Generic in C11

问题 I heard C11 added generics. I\'ve googled a bit, looked at some articles, understood there\'s a new keyword ( _Generic ) and all. But I can\'t seem to grasp it all. Is it something like the generics in C# or templates in C++? Can anyone give me a brief explanation of the C11 definition of generics, its syntax and a simple sample usage example? 回答1: This is a pretty good introduction. Here's the Overview: Generic selection is implemented with a new keyword: _Generic. The syntax is similar to a

Is type-punning through a union unspecified in C99, and has it become specified in C11?

阅读更多关于 Is type-punning through a union unspecified in C99, and has it become specified in C11?

问题 A number of answers for the Stack Overflow question Getting the IEEE Single-precision bits for a float suggest using a union structure for type punning (e.g.: turning the bits of a float into a uint32_t ): union { float f; uint32_t u; } un; un.f = your_float; uint32_t target = un.u; However, the value of the uint32_t member of the union appears to be unspecified according to the C99 standard (at least draft n1124), where section 6.2.6.1.7 states: When a value is stored in a member of an