Maintain a data structure that associates the file stream/ Computer Science
Implement popen() and pclose(). Although these functions are simplified by not requiring the signal handling employed in the implementation of system() (Section 27.7), you will need to be careful to correctly bind the pipe ends to file streams in each process, and to ensure that all unused descriptors referring to the pipe ends are closed. Since children created by multiple calls to popen() may be running at one time, you will need to maintain a data structure that associates the file stream pointers allocated by popen() with the corresponding child process IDs. (If using an array for this purpose, the value returned by the fileno() function, which obtains the file descriptor corresponding to a file stream, can be used to index the array.) Obtaining the correct process ID from this structure will allow pclose() to select the child upon which to wait. This structure will also assist with the SUSv3 requirement that any still-open file streams created by earlier calls to popen() must be closed in the new child process.
