1CSSE 332Standard Library, Storage classes, and Make<stdio.h> “Provides a simple and efficient buffered I/O interface” – from man stdio– Prototypes “standard” I/O functions (Mostly) system-independent (e.g. fprintf, fgets, feof)– Defines required types (e.g. FILE)– Defines required macros Functions are defined in “standard library”– System-dependent implementations– Linked automatically23Input and Output functions fgets(stdin,…);– Similar to scanf(…)– Safe from buffer overflow fprintf(stdout,”format”,…); – Buffered output– Equivalent to printf(“format”,…) fprintf(stderr,”…”,…); – Un-buffered output– Use for error messages.4Other useful libraries and header files <string.h>– String processing functions -- str*() & mem*() <ctype.h>– Functions for testing characters <math.h>– Mathematical functions and macros <stdlib.h>– Functions for number conversion, storage allocation, and similar tasksFinding the right library In bash:– for x in /usr/lib/*.a; do if ar t $x | grep pow&> /dev/null; then echo $x; fi; done 2> /dev/nullStorage classes Visibility: parts of source code within which variable can be referenced Lifetime: phases of execution during which variable is allocated Automatic (default for local variables)– e.g. auto int i; – Visibility: within statement block– Lifetime: execution of statement block Register– e.g. register counter = 1;– Suggestion to compiler to place variable in a register– Visibility and lifetime same as auto6More storage classes – static e.g. static int i; Visibility: statement block Lifetime: program execution Value is retained and space is de-allocated only when program (not function) terminates. Historically related to Java’s static fields7More storage classes – extern e.g. – int count; //declared in file 1 Visibility must be entire file (i.e. global)– extern int count; //used in files 2,3 … Promises compiler that variable will be visible from another compilation unit Provides type Common practice is to collect externs in a header file89enum - enumerated data types#include <stdio.h>enum month{JANUARY, /* like #define JANUARY 0 */FEBRUARY, /* like #define FEBRUARY 1 */MARCH /* … */};//In main:enum month birthMonth;if(birthMonth == JANUARY){…}/* alternatively, …. */enum month{JANUARY=1, /* like #define JANUARY 1 */MARCH=3, /* like #define MARCH 3 */FEBRUARY=2, /* … */};Note: if you use the #define, the value of JANUARY will not be visible in the debugger. An enumerated data type’s value will be.10Program with multiple files Library headers– Standard– User-definedvoid myproc();extern int gData;#include <stdio.h>#include “mypgm.h”void myproc(){int mydata = gData*2;. . . /* some code */}#include <stdio.h>#include “mypgm.h”int gData=5;int main(){ myproc();return 0;}main.cmypgm.cmypgm.h11To compile (by hand)gcc main.c mypgm.c –o runorgcc -c main.c -o main.ogcc -c mypgm.c -o mypgm.ogcc mypgm.o main.o -o runIn-class exercise Copy the makefile tutorial directory to your working environment, e.g.– scp -r [email protected]:/class/csse/csse332/0708c/Code/maketutorial temp– svn export temp maketutorial– rm –rf temp12In-class exercise (cont.) Compile main.c and author.c Link them Make a change to author.c and build the executable again Make a change to author.h and build the executable again13To compile (using a makefile) Run make (woohoo!)14In-class exercise (cont.) Run make Make a change to author.c and run make again Make a change to author.h and run make again Examine the makefile– Read the comments– Note the variables– Identify and understand the dependency rules (targets, dependencies, actions)– Note on whitespace: Targets must be followed by tabs, not spaces Actions must be preceded by tabs, not spaces– This makefile is more complicated than it needs to be, but scales well1516Tips to programming well in C Always initialize your variables before using their values (especially pointers) Don’t use pointers after freeing them Don’t return pointers to local variables of functions There are no “exceptions,” so check for errors everywhere An array is also a pointer, but its value is immutable. Compile your programs with a
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