What does `wait` return in C?
In the realm of process management in C, the `wait` function plays a crucial role in handling child processes. Understanding what `wait` returns is essential for developers to effectively manage and interpret the behavior of child processes. The `wait` function is defined in the `
The `wait` function returns an integer value that provides information about the child process that has terminated. Here’s a detailed explanation of the return values:
1. Zero or -1: If `wait` returns zero, it indicates that the calling process has received a signal and has been stopped. In this case, the return value is `-1`, and `errno` is set to `EINTR`. This means that the `wait` function was interrupted by a signal.
2. The process ID (PID) of the terminated child: If `wait` returns a positive integer, it represents the process ID of the child process that has terminated. This value can be used to identify which child process has exited.
3. -WNOHANG: If `wait` is called with the `WNOHANG` option, it returns `0` if no child processes have terminated and `-1` if an error occurs. This option is useful when you want to check if any child processes have terminated without blocking the calling process.
4. -WUNTRACED: If `wait` is called with the `WUNTRACED` option, it returns the PID of the child process that has been stopped but not terminated (e.g., stopped by a signal). If no child process is stopped, it returns `-1`.
It’s important to note that the `wait` function clears the process status information for the terminated child process. If you need to retrieve the exit status of the child process, you can use the `WIFEXITED` and `WEXITSTATUS` macros from the `
In conclusion, understanding what `wait` returns in C is vital for managing child processes effectively. By interpreting the return values correctly, developers can ensure that their programs can handle child process termination and signaling events appropriately.
