Perl is more like Java. It's compiled, turned into an internal format (called "the optree") and then executed in its own virtual machine. The difference with Java is that in Java, compiling is a separate action from running the program - in Perl, compiling is the first stage of running.
Now, for the long answer, the fact that C gets compiled to a native binary and then executed and Perl gets compiled to an optree counts for some difference, but far from all. Even if there was a Perl compiler that turned out native binaries (say there would be a Perl front end to the gcc compiler), then the Perl program would still be much slower than the C program. It's the price you pay for flexibility. In C, if you have an 'int' variable, that you just have an integer. C can just allocate 4 (or 8) bytes and it will know there's always an integer there. Perl doesn't. In Perl, if you access a variable and use it like an int, Perl will first fetch the meta data. It'll test whether the value stored is valid as an integer. Getting that integer requires another fetch (pointer + offset). If the value isn't valid as an integer, it will first have to calculate the integer value, from the string value for instance.
Perl values (and hence, variables) come will all kinds of neat tricks. Strings become integers/floats and the other way around magically. Strings can expand in length without the programmer having to create a new variable. Variables can be tied, blessed or have some other magic attached. For all this niceness, you have to pay a price. And that prices doesn't only come in the form of memory usage. You pay a hefty runtime price as well.
In reply to Re^2: Why is this code so much slower than the same algorithm in C?
by JavaFan
in thread Why is this code so much slower than the same algorithm in C?
by wanna_code_perl
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