Designated initializers

Use case

Initialize structs by field name for clarity.

Explanation

Name fields explicitly. Order must match declaration. Unspecified fields are zero-initialized.

Code

#include <cstdint>
#include <iostream>

// https://en.wikipedia.org/wiki/Mach-O
struct MachHeader64 {
  uint32_t magic;
  // uint32_t cputype;
  // uint32_t cpusubtype;
  uint32_t filetype;
  uint32_t numofcmds;
  // uint32_t sizeofcmds;
  // uint32_t flags;
  // uint32_t reserved;
};

int main() {
  MachHeader64 hdr{
      .magic = 0xFEEDFACF,
      .filetype = 0x2, // MH_EXECUTE
      .numofcmds = 0x0,
  };

  std::cout << "Magic: 0x" << std::hex << hdr.magic << "\n";
  std::cout << "Num of cmds: " << std::dec << hdr.numofcmds << "\n";

  return 0;
}

View on GitHub.

Output

$ ./src/c++20/build/designated-initializers
Magic: 0xfeedfacf
Num of cmds: 0