Searching information in one file or in multiple files

One file at a time vs. searching files for information

There are 2 approaches to program compilation:

Compile only what you are told to compile (= translate)
Compile as much as possible:

The java compiler: compiles as much as it can...

The Java compiler:

When you compile a Java program prog.java
The Java compiler will search in other program files for missing information

Example:

public class prog { public static void main(String[] args) { int a, b; a = 2; b = prog2.f( a ); // f( ) is defined in ANOTHER Java program file !!! } }
public class prog2 { public static float f ( float x ) { return x*x; } }

When you compile the program prog.java:

javac prog.java

The Java compiler will automatically search for missing information in the file prog2.java

Demo:

cd /home/cs255000/demo/c/Compiler javac prog.java

The C compiler: compiles only what user wants (total control)...

The C compiler:

When you compile a C program prog.c
The C compiler will only look inside the (one) specified program file for program information

Example:

prog.c: int main(int argc, char *argv[]) { int a, b; a = 2; b = f( a ); // f( ) is defined in ANOTHER C program file !!! } }
prog2.c: float f ( float x ) { return x*x; } }

When you compile the program prog.c:

gcc prog.c

The Java compiler will report an error:

cs255 (1732)> gcc prog.c /tmp/ccSbeAWZ.o: In function `main': prog.c:(.text+0x21): undefined reference to `f' (Because the C compiler cannot find f( ) in the file !!!)

Demo:

cd /home/cs255000/demo/c/Compiler gcc prog.c