Если у вас много файлов в проекте,их не нужно перекомпилировать все ,если изменения сделаны в одном.
В следующем примере показано,что цель pgm зависит от a.o и b.o , а те в свою очередь зависят от
a.c и b.c :
pgm: a.o b.o
cc -Aa a.o b.o -o pgm
a.o: incl.h a.c
cc -Aa -c a.c
b.o: incl.h b.c
cc -Aa -c b.c
Следующий пример для программы dtree . Вначале создаются несколько переменных .
#include "stdio.h"
char *words[]={"apple","belt","corpus","daffodil","epicycle","floppy",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"glands","handles","interfere","jumble","kick","lustiness",
"mangleworsel","nefarious","oleangeous","parsimonious",NULL};
void slow(void)
{
int i,j,count=0;
for (i=0; words[i] != NULL ; i=i+1)
for (j=0; j <= strlen(words[i]) ; j=j+1)
if(words[i][j] == words[i][j+1])
count= count+1;
printf("count %d\n",count);
}
void fast(void)
{
register char **cpp; /* cpp is an array of pointers to chars */
register char *cp;
register int count=0;
for (cpp= words; *cpp ; cpp++) /* loop through words. The final
NULL pointer terminates the loop */
for (cp = *cpp ; *cp ; cp++) /* loop through letters of a word.
The final '\0' terminates the loop */
if(*cp == *(cp+1))
count++;
printf("count %d\n",count);
}
/*count the number of double letters, first using arrays, then pointers */
void main(int argc, char *argv[]){
slow();
fast();
}
A data filter
Программа распечатывает содержимое ASCI-файла,состоящего из последовательности чисел.
#include < stdio.h>
#include < stdlib.h>
int answer;
float offset;
float scale;
char buf[BUFSIZ];
int xcoord = 0;
char *cptr;
int transform(int a)
{
return a * scale + offset + 0.5;
}
char* eat_space(char *cptr){
/* This while loop skips to the nonspace after spaces.
If this is the end of the line, return NULL
`While a space, keep going'
*/
while (*cptr ==' '){
if (*cptr == '\0')
return NULL;
else
cptr++;
}
return cptr;
}
char * next_next_num(char *cptr){
/* This while loop skips to the 1st space after a number.
If this is the end of the line, return NULL
`While NOT a space, keep going'
*/
while (*cptr !=' '){
if (*cptr == '\0')
return NULL;
else
cptr++;
}
/* Now move to the start of the next number */
return eat_space(cptr);
}
int main(int argc, char *argv[])
{
offset = 2.3;
scale = 7.5;
while(1){
/* if we haven't reached the end of the file ...*/
if(fgets(buf, BUFSIZ,stdin)!= NULL){
/* initialise cptr to point to the first number ...*/
cptr = eat_space(buf);
do{
/* convert the representation of the num into an int */
sscanf(cptr,"%d", &num);
/* print x and y to stdout */
printf("%d %d\n",xcoord, tranform(num));
/* skip to the start of the next number on the line */
cptr=next_next_num(cptr);
xcoord++;
}while ( cptr!=NULL);
}
else{
exit(0);
}
}
}
Чтение директорий.
#include < stdio.h>
#include < sys/types.h>
#include < dirent.h>
#include < sys/stat.h>
#define REQUEST_DIR "/"
int main(int argc, char *argv[]){
FILE *fp;
DIR *dirp;
struct dirent *dp;
struct stat buf;
dirp = opendir(REQUEST_DIR);
chdir(REQUEST_DIR);
/* Look at each entry in turn */
while ((dp = readdir(dirp)) != NULL) {
/* Now stat the file to get more information */
if (stat(dp->d_name, &buf) == -1)
perror("stat\n");
if (S_ISDIR(buf.st_mode))
printf("%s is a directory\n", dp->d_name);
else if (S_ISREG(buf.st_mode))
printf("%s is a regular file\n", dp->d_name);
}
(void) closedir(dirp);
}
Многомерные массивы.
Элементы массива aai[4][2] хранятся в памяти в следующем порядке :
aai[0][0]aai[0][1]aai[1][0]aai[1][1]
aai[2][0]aai[2][1]aai[3][0]aai[3][1]
При этом
aai[1][2] == *( (aai[1])+2) == *(*(aai+1)+2)
Realloc
#include < stdlib.h>
int *array = NULL;
int nalloc = 0;
int num_of_elements = 0;
install(x)
int x;
{
if(num_of_elements >= nalloc){
/* We're out of space. Reallocate with space for 10 more ints */
nalloc += 10;
array = (int *)realloc((char *)array, nalloc * sizeof(int));
if(array == NULL){
fprintf(stderr, "out of memory with %d elements\n",
num_of_elements);
exit(1);
}
}
array[num_of_elements++] = x;
}
Вариант для 2-мерного массива:
/* create an array of pointers */
int **array = (int **)malloc(nrows * sizeof(int *));
if (array == NULL){
fprintf(stderr,"Out of memory\n");
exit(1);
}
for(i = 0; i < nrows; i++){
/* create space for an array of ints */
array[i] = (int *)malloc(ncolumns * sizeof(int));
if (array[i] == NULL){
fprintf(stderr,"Out of memory\n");
exit(1);
}
}
Signals and error
Программа может получать различные сигналы(или прерывания) . Их можно обрабатывать или игнорировать.
#include < signal.h>
/* this will ignore control-C */
signal(SIGINT, SIG_IGN);
В следующем примере используется прерывание по таймеру.
Сначала нужно вызвать Timer , который вызовет прерывание :
#include < signal.h>
static void onalarm(void)
{
something();
signal(SIGALRM,SIG_DFL);
}
...
void Timer(int n) /* waits for 'n' milliseconds */
{
long usec;
struct itimerval it;
if (!n) return;
usec = (long) n * 1000;
memset(&it, 0, sizeof(it));
if (usec>=1000000L) { /* more than 1 second */
it.it_value.tv_sec = usec / 1000000L;
usec %= 1000000L;
}
it.it_value.tv_usec = usec;
signal(SIGALRM,onalarm);
setitimer(ITIMER_REAL, &it, (struct itimerval *)0);
}
LINUX 
Languages
