unix

问题 This is from The GNU C Library Reference Manual int SIGFPE The SIGFPE signal reports a fatal arithmetic error. This signal actually covers all arithmetic errors, including division by zero and overflow. BSD systems provide the SIGFPE handler with an extra argument that distinguishes various causes of the exception. In order to access this argument, you must define the handler to accept two arguments, which means you must cast it to a one-argument function type in order to establish the

问题 This is from The GNU C Library Reference Manual int SIGFPE The SIGFPE signal reports a fatal arithmetic error. This signal actually covers all arithmetic errors, including division by zero and overflow. BSD systems provide the SIGFPE handler with an extra argument that distinguishes various causes of the exception. In order to access this argument, you must define the handler to accept two arguments, which means you must cast it to a one-argument function type in order to establish the

问题 On Unix (Clang 3.8.1), this code outputs: 6: 32 8: a8e On Windows (MSVC 19.00.24215.1), this code outputs: 6: 12345 6: a12345e #include <iostream> #include <stdarg.h> static std::string getFormattedString(const char* fmt, va_list ap) { int count = vsnprintf(NULL, 0, fmt, ap) + 1; std::cout << count << ": "; if (count <= 0) { return "unable to format message"; } std::string result = std::string(count, '\0'); if (vsnprintf(&result[0], count, fmt, ap) < 0) { return "error";} return result; }

问题 How to access bash positional parameter through a variable? e.g. I have a variable "pos", which can be anything between 1 to 6 (say). If pos==1 , I want to do: echo $1 If pos==2 , I want to do: echo $2 So on. Intuitively, I want to do something like: echo $$pos . I want to do it in one line. 回答1: Use variable indirection: echo "${!pos}" 回答2: Here are several solutions. Some may need a recent version of bash , others may still work with a very old one. Let us set up first our environment... $

问题 I am reading data from multiple serial ports. At present I am using a custom signal handler (by setting sa_handler) to compare and wake threads based on file descriptor information. I was searching for a way out to have individual threads with unique signal handlers, in this regard I found that select system call is to be used. Now I have following questions: If I am using a thread (Qt) then where do I put the select system call to monitor the serial port? Is the select system call thread

问题 I am reading data from multiple serial ports. At present I am using a custom signal handler (by setting sa_handler) to compare and wake threads based on file descriptor information. I was searching for a way out to have individual threads with unique signal handlers, in this regard I found that select system call is to be used. Now I have following questions: If I am using a thread (Qt) then where do I put the select system call to monitor the serial port? Is the select system call thread

问题 I would like to know what does the command source do. I have tried: whatis $ whatis source source: nothing appropriate. man $ man source No manual entry for source source (-h, --help, etc...) $ source source: not enough arguments But it seems no documentation about it. I commonly use it to save any changed on my dotfiles, but what does it exactly do? Why there is not documentation about it? 回答1: source is a bash shell built-in command that executes the content of the file passed as an

问题 I would like to know what does the command source do. I have tried: whatis $ whatis source source: nothing appropriate. man $ man source No manual entry for source source (-h, --help, etc...) $ source source: not enough arguments But it seems no documentation about it. I commonly use it to save any changed on my dotfiles, but what does it exactly do? Why there is not documentation about it? 回答1: source is a bash shell built-in command that executes the content of the file passed as an

问题 I would like to know what does the command source do. I have tried: whatis $ whatis source source: nothing appropriate. man $ man source No manual entry for source source (-h, --help, etc...) $ source source: not enough arguments But it seems no documentation about it. I commonly use it to save any changed on my dotfiles, but what does it exactly do? Why there is not documentation about it? 回答1: source is a bash shell built-in command that executes the content of the file passed as an

问题 I would like to know what does the command source do. I have tried: whatis $ whatis source source: nothing appropriate. man $ man source No manual entry for source source (-h, --help, etc...) $ source source: not enough arguments But it seems no documentation about it. I commonly use it to save any changed on my dotfiles, but what does it exactly do? Why there is not documentation about it? 回答1: source is a bash shell built-in command that executes the content of the file passed as an