text: #include <seqan/basic.h>
  #include <seqan/seq_io.h>
  #include <seqan/sequence.h>
  
  using namespace seqan;
  
  int main()
  {
      CharString path = getAbsolutePath("/demos/dox/seq_io/example.fa");
  
      FaiIndex faiIndex;
  
      // Try to read the FAI index.
      if (!open(faiIndex, toCString(path)))
      {
          std::cerr << "Could not read the FAI index.  Not fatal, we can just build it.\n";
          return 1;
      }
  
      // Try to build the FAI index (in memory) if reading was unsuccessful.  If
      // building into memory succeeded, we try to write it out.
      if (!build(faiIndex, toCString(path)))
      {
          std::cerr << "FATAL: Could not build FAI index.\n";
          return 1;
      }
  
      if (!save(faiIndex))
      {
          std::cerr << "FATAL: Could not write out FAI index after building.\n";
          return 1;
      }
  
      // Now, read the first 1000 characters of chr1.
      unsigned idx = 0;
      if (!getIdByName(idx, faiIndex, "chr"))
      {
          std::cerr << "FATAL: chr1 not found in FAI index.\n";
          return 1;
      }
      CharString seq;
      readRegion(seq, faiIndex, idx, 0, 100);
  
      // Now print the first 100 characters we just read.
      std::cout << "chr:1-100 = " << seq << "\n";
  
      return 0;
  }
  