一个简单的alarm实例
errors.h头文件
#ifndef __ERRORS_H
#define __ERORRS_H #include<stdio.h>
#include<unistd.h>
#include<errno.h>
#include<stdlib.h>
#include<string.h> #ifdef DEBUG
#define DPRINTF(arg) printf arg
#else
#define DPRINTF(arg)
#endif #define err_abort(code, text) do { \
fprintf(stderr, "%s at \"%s\":%d: %s\n", \
text, __FILE__, __LINE__, strerror(code)); \
abort(); \
} while() #define errno_abort(text) do { \
fprintf(stderr, "%s at \"%s\":%d: %s\n", \
text, __FILE__, __LINE__, strerror(errno));\
abort();\
}while() #endif
errors.h
普通实现：alarm.c
#include"errors.h" /* alarm的普通实现 */
int main(int argc, char* argv[])
{
int seconds;
char line[];
char message[]; while()
{
printf("Alarm> ");
if(fgets(line, sizeof(line), stdin) == NULL ) exit();
if(strlen(line) <= ) continue;
if(sscanf(line, "%d %64[^\n]", &seconds, message) < )
fprintf(stderr, "Bad command\n");
else
{
sleep(seconds);
printf("(%d) %s\n", seconds, message);
} }
}
alarm.c
多进程实现：alarm_fork.c
#include "errors.h"
#include<sys/types.h>
#include<wait.h> /* alarm的多进程实现 */
int main(int argc, char* argv[])
{
int status;
char line[];
int seconds;
pid_t pid;
char message[]; while()
{
printf("Alarm> ");
if(fgets(line, sizeof(line), stdin) == NULL ) exit();
if(strlen(line) <= ) continue;
if(sscanf(line, "%d %64[^\n]",
&seconds, message) < )
{
fprintf(stderr, "Bad command\n");
}
else
{
pid = fork();
if(pid == (pid_t)-)
errno_abort("fork");
if(pid == (pid_t))
{
sleep(seconds);
printf("(%d) %s\n", seconds, message);
exit();
}
else
{
do
{
pid = waitpid((pid_t)-, NULL, WNOHANG);
if(pid == (pid_t)-)
errno_abort("wait child");
}while(pid != (pid_t));
}
}
}
}
alarm_fork.c
多线程实现：alarm_thread.c
#include<pthread.h>
#include "errors.h" /* alarm的多线程实现 */ typedef struct alarm_tag {
int seconds;
char message[];
} alarm_t; void * alarm_thread(void *arg)
{
alarm_t *alarm = (alarm_t*)arg;
int status; status = pthread_detach(pthread_self());
if( status != )
err_abort(status, "pthread_detach");
sleep(alarm->seconds);
printf("(%d) %s\n", alarm->seconds, alarm->message);
free(alarm);
return NULL;
} int main(int argc, char* argv[])
{
int status;
char line[];
alarm_t *alarm;
pthread_t thread; while()
{
printf("Alarm> ");
if(fgets(line, sizeof(line), stdin ) == NULL ) exit();
if(strlen(line) <= ) continue;
alarm = (alarm_t*)malloc(sizeof(alarm_t));
if( alarm == NULL )
errno_abort("malloc");
if( sscanf(line, "%d %64[^\n]",
&alarm->seconds, alarm->message) < )
{
fprintf(stderr, "Bad command\n");
free(alarm);
}
else
{
status = pthread_create(&thread, NULL, alarm_thread, alarm);
if( status != )
err_abort(status, "pthread_creat");
}
}
}
alarm_thread.c
在以上alarm_thread.c代码执行时候，发现如果输入正好是128-1的倍数，将会出现Bad Command的提示。
追究下原因，原来是fgets导致：
fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading stops after an EOF or
a newline. If a newline is read, it is stored into the buffer. A terminating null byte ('\0') is stored after the last character in the buffer.
#include<stdio.h>
#include<unistd.h>
#include<error.h>
#include<stdlib.h> void main(void)
{
char line[];
char* message; while()
{
printf("INPUT> ");
if(fgets(line, sizeof(line), stdin ) == NULL ) exit();
message = (char*)malloc();
if( sscanf(line, "%2[^\n]",
message) < )
{
fprintf(stderr, "sscanf error.\n");
}
else
{
printf("message: %s\n", message);
}
free(message);
}
} /*
*root@jdu-virtual-machine:~# ./a.out
*INPUT> aaa
*message: aa
*sscanf error.
*INPUT> INPUT> ^C
*/
Breakpoint at 0x4007ca: file test.c, line .
(gdb) r
Starting program: /root/a.out
INPUT> aaa Breakpoint , main () at test.c:
message = (char*)malloc();
(gdb) p line
$1 = "aaa"
(gdb) n
if( sscanf(line, "%2[^\n]",
(gdb)
printf("message: %s\n", message);
(gdb) p message
$2 = 0x602010 "aa"
(gdb) n
message: aa
free(message);
(gdb)
}
(gdb)
printf("INPUT> ");
(gdb)
if(fgets(line, sizeof(line), stdin ) == NULL ) exit();
(gdb) Breakpoint , main () at test.c:
message = (char*)malloc();
(gdb) p line
$3 = "\n\000a"
(gdb) n
if( sscanf(line, "%2[^\n]",
(gdb)
fprintf(stderr, "sscanf error.\n");
(gdb)
sscanf error.
free(message);
(gdb)