MPI_File_seek - C++

MPI_File_seek is a function in MPI (Message Passing Interface) that allows you to seek within a file opened with MPI_File_open. This function is used to change the position of a file pointer within the file associated with a communicator.

Syntax

int MPI_File_seek(MPI_File fh, MPI_Offset offset, int whence)

• fh : file handle (handle)
• offset : offset in bytes (integer)
• whence : initial position (integer)

Parameters

• fh - File handle (handle).
• offset - Offset in bytes relative to whence. The offset can be positive or negative (integer).
• whence - Whence is the initial position indicator. It can take one of the following values:
  • MPI_SEEK_SET - Start the offset from the beginning of the file.
  • MPI_SEEK_CUR - Start the offset from the current position in the file.
  • MPI_SEEK_END - Start the offset from the end of the file.

Return value

• On success, this function returns MPI_SUCCESS.
• On error, this function returns an error code.

Example Usage

Below is an example usage of MPI_File_seek. In this example, we open a file using MPI_File_open and then seek to the end of the file.

MPI_File fh;
MPI_Status status;
int myrank;
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

MPI_File_open(MPI_COMM_WORLD, "testfile", MPI_MODE_RDWR, MPI_INFO_NULL, &fh);

MPI_Offset filesize;
MPI_File_get_size(fh, &filesize);

// Seek to end of file
MPI_File_seek(fh, filesize, MPI_SEEK_SET);

MPI_File_close(&fh);

Conclusion

MPI_File_seek is a useful function in MPI that allows you to change the position of a file pointer within the file associated with a communicator. It provides a way to efficiently manipulate file pointers and perform file operations in parallel.