How do I use mmap for fast I/O in C++?

mmap is a powerful mechanism that allows you to map a file or device into memory. In C++, it can be used for fast I/O by providing direct access to the file's contents, enabling efficient reading and writing without the overhead of traditional I/O calls.

Using mmap for Fast I/O in C++

To use mmap in C++, follow these steps:

  1. Include necessary headers:
    2. #include <sys/mman.h> #include <fcntl.h> #include <unistd.h> #include <sys/types.h> #include <iostream> #include <cstring>
  2. Open the file using open() to get the file descriptor.
  3. Use mmap() to map the file into memory.
  4. Access the data directly through the pointer returned by mmap().
  5. Don't forget to unmap the memory and close the file descriptor after usage.

Example Code

#include <sys/mman.h> #include <fcntl.h> #include <unistd.h> #include <sys/types.h> #include <iostream> #include <cstring> int main() { const char *fileName = "example.txt"; int fd = open(fileName, O_RDWR); if (fd == -1) { std::cerr << "Error opening file." << std::endl; return 1; } size_t fileSize = lseek(fd, 0, SEEK_END); lseek(fd, 0, SEEK_SET); char *mapped = (char *)mmap(NULL, fileSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); if (mapped == MAP_FAILED) { std::cerr << "Error mapping file." << std::endl; close(fd); return 1; } // Perform read/write operations on the mapped memory std::cout << "File content: " << std::string(mapped, fileSize) << std::endl; strcpy(mapped, "New content written to file\n"); // Writes directly to file // Clean up munmap(mapped, fileSize); close(fd); return 0; }

mmap fast I/O C++ memory mapping file I/O performance optimization

Related Questions

How do I avoid rehashing overhead with std::set in multithreaded code?

How do I find elements with custom comparators with std::set for embedded targets?

How do I erase elements while iterating with std::set for embedded targets?

How do I provide stable iteration order with std::unordered_map for large datasets?

How do I reserve capacity ahead of time with std::unordered_map for large datasets?

How do I erase elements while iterating with std::unordered_map in multithreaded code?

How do I provide stable iteration order with std::map for embedded targets?

How do I provide stable iteration order with std::map in multithreaded code?

How do I avoid rehashing overhead with std::map in performance-sensitive code?

How do I merge two containers efficiently with std::map for embedded targets?