C++ variant of cpu-api/p4.c (Figure 5.4)

Makefile

CXXFLAGS = -g -std=c++17 -Wall -Wextra -Wpedantic -Werror

all: p4

# Note: using implicit rule for .cpp files to create p4

.PHONY: clean test

test: p4
	./p4 && cat p4.output

clean:
	rm -f p4 p4.output

p4.cpp

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>

#include <vector>

#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>

using std::vector;

int
main(int argc, char *argv[])
{
    (void)argc, (void)argv;

    auto rc = fork();
    if (rc < 0) {
        // fork failed; exit
        perror("fork failed");
        exit(EXIT_FAILURE);
    } else if (rc == 0) {
        // child: redirect standard output to a file
        close(STDOUT_FILENO);
        open("./p4.output", O_CREAT | O_WRONLY | O_TRUNC, S_IRWXU);

        // now exec "wc"...
        vector<char *> myargs;
        myargs.push_back(strdup("wc"));     // program: "wc" (word count)
        myargs.push_back(strdup("p4.cpp")); // argument: file to count
        myargs.push_back(NULL);             // marks end of array
        execvp(myargs[0], myargs.data());   // runs word count
    } else {
        // parent goes down this path (original process)
        auto wc = wait(NULL);
        assert(wc >= 0);
    }
    return EXIT_SUCCESS;
}