如何从文本文件中读取带有mmap的双打数组

Question

I tried this:

double *mat = (double *) mmap(NULL, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);

where sb.st_size is the size of the file and fd is the descriptor of the opened file. If I want to iterate through all the elements I get only 0s, but the file has only non 0 values. What is wrong with this?

Answer 1

You cannot.

If you truly have a text file, then you have text numbers, almost like a spreadsheet:

1.0 2.0 3.0
1.1 2.1 3.1

You cannot mmap that file and treat the mapped memory as double* , because that is character data.

In order to convert the file from character data to doubles, you will have to do something like fscanf or scanf to process the digits.

On the other hand, if you wrote out a blob of doubles as binary data, then you could do the mmap , pretty much as you describe.