|
 |
 |
 |
 |
 |
 |
 |
 |
 |
4.6.5.1 MPfile links
MPfile links provide the possibility to store data in a file using the binary MP format. Read and write operations are very fast compared to ASCII links. Therefore, for storing large amounts of data, MPfile links should be used instead of ASCII links. Unlike ASCII links, data read from MPfile links is returned as expressions one at a time, and not as a string containing the entire content of the file. Furthermore, ring-dependent data is stored together with a ring description. Therefore, reading ring-dependent data might change the current ring.
The MPfile link describing string has to be one of the following:
-
"MPfile: "+ filename
the mode (read or append) is set by the firstreadorwritecommand. -
"MPfile:r "+ filename
opens the file for reading. -
"MPfile:w "+ filename
opens the file for overwriting. -
"MPfile:a "+ filename
opens the file for appending.
There are the following default values:
- if none of
r,w, orais specified, the mode of the link is set by the firstreadorwritecommand on the link. If the first command iswrite, the mode is set toa(append mode).
Note that the filename may contain a path. An MPfile link can be used
either for reading or for writing, but not for both at the same time. A
close command must be used before a change of I/O direction.
Example:
ring r;
link l="MPfile:w example.mp"; // type=MPfile, mode=overwrite
l;
→ // type : MPfile
→ // mode : w
→ // name : example.mp
→ // open : no
→ // read : not ready
→ // write: not ready
ideal i=x2,y2,z2;
write (l,1, i, "hello world");// write three expressions
write(l,4); // append one more expression
close(l); // link is closed
// open the file for reading now
read(l); // only first expression is read
→ 1
kill r; // no basering active now
def i = read(l); // second expression
// notice that current ring was set, the name was assigned
// automatically
listvar(ring);
→ // mpsr_r0 [0] *ring
def s = read(l); // third expression
listvar();
→ // s [0] string hello world
→ // mpsr_r0 [0] *ring
→ // i [0] ideal, 3 generator(s)
→ // l [0] link
→ // LIB [0] string standard.lib
close(l); // link is closed
dump("MPfile:w example.mp"); // dump everything to example.mp
kill i, s; // kill i and s
getdump("MPfile: example.mp");// get previous dump
listvar(); // got all variables and values back
→ // mpsr_r0 [0] *ring
→ // i [0] ideal, 3 generator(s)
→ // s [0] string hello world
→ // l [0] link
→ // LIB [0] string standard.lib
|