1 include"" 和include<>区别。
前者在当前目录下找头文件，找不到再到系统目录下找，而include<>，直接在系统目录下找。所以include""涵盖了include<>
2.incline 声明函数，表示内联函数，内联函数即在调用处直接展开函数，而并非取调用函数，故不用保存现场，效率得到提高
3 宏定义简单函数，如#define TABLE_COMP(x) ((x)>0?(x):0)
优点:若函数调用，则要将函数的执行顺序转移到函数所存放的某个地址，将函数程序内容执行完后，在返回到转去执行原函数，故要保护现场。所以函数调用有时间、空间的开销，效率低。而宏是在预处理的地方把代码展开，五上述额外时间、空间开销。
缺点：容易产生二义性 如TABLE_MULTI(10+10)会(10+10*10+10)，而非期望的400
4.递归代码简介，但缺点（1）递归是函数调用自身，函数调用存在时间消耗：每一次函数调用，需要在内存栈中分配空间以保存参数、返回地址及临时变量，栈的压入和弹出都需要时间。故递归实现不如循环。（2）调用栈溢出。每一次调用在内存栈中分配空间，每个进程栈的容量有限，若递归调用的层级太多，就会溢出
5.计算机表示小数（float和double）都有误差，故不能直接用等号判断两个小数是否相等。如果两个小数的差值很小，比如0.0000001，就可以认为它们相等
6.取模操作 % 操作数两边都应该为整形 如 12%3 （对） 2.2%1 （错） 2%1.1（错） 2.2%1.1（错）
7 float = int/int 则除出来的数已经自动省掉了小数点后面的余数。如 f1=int1/1024，可以改为 f1=int1/1024.0
8.sleep()内的单位为秒，gcc编译，在头文件#include<unistd>中
9.若要获取运行程序进程号，linux除了通过ps指令外。还可以通过getpid函数，该函数也在unistd.h中
/*process.c*/
#include <unistd.h>
#include <pwd.h>
#include <sys/types.h>
#include <stdio.h>
int main(int argc, char **argv)
{
pid_t my_pid,parent_pid;
uid_t my_uid,my_euid;
gid_t my_gid,my_egid;
struct passwd *my_info;
my_pid = getpid();
parent_pid = getppid();
my_uid = getuid();
my_euid = geteuid();
my_gid = getgid();
my_egid = getegid();
}
10 strcmp函数使用strcmp("sundayhut",myname);注意不要写成strcmp("sundayhut\n",myname);
11 sscanf用法
sscanf(temp,"%s%s%s%s%s%s%s%[^\n]",last_major_minor,last_cpu_id,last_sequence_number,last_time,last_process_id,last_action,last_RWBS,last_detail);
读入文件形式如下：
8,0 0 1 0.000000000 2113 A W 38384096 + 8 <- (8,1) 38382048 8,1 0 2 0.000001649 2113 Q W 38384096 + 8 [blktrace_study] 8,1 0 3 0.000055171 2113 G W 38384096 + 8 [blktrace_study] 8,1 0 4 0.000234077 2113 P N [blktrace_study] 8,1 0 5 0.000362702 2113 I W 38384096 + 8 [blktrace_study] 8,1 0 0 0.000362704 0 m N cfq640 insert_request 8,1 0 0 0.000362705 0 m N cfq640 add_to_rr 8,0 0 6 0.000362707 2113 A W 38384104 + 8 <- (8,1) 38382056 8,1 0 7 0.000362709 2113 Q W 38384104 + 8 [blktrace_study]
%s能自动过滤掉空格，%[^\n]可以读入行直到行尾部
12.若open函数用O_DIRECT方式fd=open("/home/systemtap_study/dir1/25.txt", O_RDWR | O_CREAT | O_DIRECT);
则在*.c文件中需要
#define __USE_GNU
且编译时需要加上-D_GNU_SOURCE
gcc -o out code.c -D_GNU_SOURCE
13.打印unsigned long
unsigned long block;
printk("new block %lu\n",block);
14.编译错误
编译出现如下错误
/home/tss/share/7-7/printk-pcmfs/pcmfs/pcmfs/inode.c:417: warning: ISO C90 forbids mixed declarations and code
iso c90 不允许混合使用声明和代码
解决方法是，printk语句不能再变量声明前使用
例如：void fun（）
{
printf（"This is a strange World!\n"）;
int i;
char buf[128];
}
改正方法：
void fun（）
{
int i;
char buf[128];
printf（"This is a strange World!\n"）;
}
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