对于系统调用IO接口的具体理解(详细!!!!!)

Myth丶恋晨 2022-11-13 06:27 167阅读 0赞

![在这里插入图片描述][202103261110095.png]

### 系统调用IO接口 ###

*  目录:
 *   *  1.open
     *  2.write
     *  3.read
     *  4.lseek
     *  5.close

# 目录: #

## 1.open ##

这里是一个打开文件的操作,且对于被flags的操作我们可以通过或的方式对多个操作进行叠加  
 int open(const char\* pathname,int flags,mode\_t mode);   
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NjU1NDU4Mg_size_16_color_FFFFFF_t_70]  
**举例:**

int  fd=int open("./test";O_RDWR;0777);

## 2.write ##

ssize\_t write(int fd,const void \*buf,size\_t count);

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NjU1NDU4Mg_size_16_color_FFFFFF_t_70 1]  
**举例:**

char* ptr="123456";
    
    int ret = write(fd, ptr, strlen(ptr));

## 3.read ##

ssize\_t read(int fd,void \*buf,size\_t count);

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NjU1NDU4Mg_size_16_color_FFFFFF_t_70 2]

**举例:**

char buf[1024] = {  0 };
    
    ret = read(fd, buf, 1023);

## 4.lseek ##

off\_t lseek(int fd,off\_t offset,int whence);   
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NjU1NDU4Mg_size_16_color_FFFFFF_t_70 3]  
**举例:**

//lseek(句柄，偏移量，位置) SEEK_SET SEEK_CUR SEEK_END
    	lseek(fd, 0, SEEK_SET);

## 5.close ##

int close(int fd);

**fd:利用对应的操作句柄对于这个文件进行关闭**  
**举例:**

close(fd);

这里就是对于系统调用接口的具体理解,关于这些接口,我们多练练就会了.

[202103261110095.png]: /images/20221022/e6ad0d1c119d4c1fba6b3762a687c7df.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NjU1NDU4Mg_size_16_color_FFFFFF_t_70 1]: /images/20221022/cdefe5a20eb244ada16c5663465e3ee7.png
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NjU1NDU4Mg_size_16_color_FFFFFF_t_70 3]: /images/20221022/d617b7ac85294c73a24813e933df934f.png