C++ Program to find a string in a file. Use `strfind file text` to search for <text> in <file>

strfind.cpp

extern "C" {
#include <sys/mman.h>
#include <fcntl.h>
}
    
#include <cstring>
#include <cerrno>
#include <iostream>
    
int main(int argc, char* argv[]) {
      
	// I don't check the arguments here, you should probably do that
    	
	// String to search for
	char* search_string = argv[2];
    	
	// Open the file so we can map it
	int fd = open(argv[1], O_RDONLY);
	if (fd < 0) {
		std::cout << "Open failed: " << strerror(errno) << std::endl;
		return 1;
	}
    	
	// Find the length of the file so we know how much to map
	off_t len = lseek(fd, 0, SEEK_END);
	if (len == -1) {
		std::cout << "Seek failed: " << strerror(errno) << std::endl;
		return 1;
	}
    	
	// map the file into memory
	char* file_contents = (char*)mmap(
		NULL, len, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0);
	if (file_contents == MAP_FAILED) {
		std::cout << "map failed: " << strerror(errno) << std::endl;
		return 1;
	}
    	
	// We don't need the file open any more, we do need to unmap it later though
	close(fd);
    	
	// Search for the string in the file here
	char* found = strnstr(file_contents, search_string, len);
	if (found == NULL)
		std::cout << "String not found" << std::endl;
	else
		std::cout << "String found @ " << found - file_contents << std::endl;
    		
	munmap(file_contents, len);
}

compile it with $ clang strfind.cpp -ostrfind