Cirrus Logic CS485 Bedienungsanleitung PDF herunterladen (Seite 38)

CS485G Spring 2015 38

6. Advice:

(a) Multiple compilation units should share global declarations via

a .h ﬁle.

(b) Use static if possible to prevent conﬂicts.

(d) Declare shared global variables extern.

41 Libraries

1. Lecture 22, 3/25/2015

2. C library (libc): about 4MB (static), 2MB (dynamic); about 1600

symbols; routines for I/O, memory allocation, signals, strings, ran-

dom numbers, integer mathematics.

3. Math library (libm): about 1MB; about 400 symbols; ﬂoating-point

math.

4. The linker only uses the symbols from the library that are unresolved

when it gets to that library in the command-line order, so libraries

should be listed at the end of the command line, and special libraries

(like libm) before general ones (like libc).

5. Shared libraries that are dynamically loaded reduce duplication in

executable object ﬁles and allow for quick incorporation of bug ﬁxes.

6. Shared libraries are usually loaded into memory when a program

starts, but it is possible to load them later.

1 #include <dlfcn.h>

2 void

handle;

3 void (

addvec)(int

, int

, int);

4 char

error;

5 handle = dlopen("./libvector.so", RTLD_LAZY);

6 // should verify handle != NULL

7 addvec = dlsym(handle, "addvec");

8 // should verify addvec != NULL

9 // may now invoke addvec()

10 dlclose(handle);; // should verify return value >= 0

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Cirrus Logic CS485 Bedienungsanleitung Seite 38