库函数和 系统调用

1：系统调用

#include
#include
#include
#include
#include#define  BUFFER_SIZE  100
char * str_a = "C:\\Users\\jiang000\\CLionProjects\\systemCall\\a";
char * str_b = "C:\\Users\\jiang000\\CLionProjects\\systemCall\\b";int main(){int a_fd = open(str_a,O_RDONLY);printf("%d",a_fd);long size = lseek(a_fd,0,SEEK_END);long half_size = size / 2;long res = lseek(a_fd,-half_size,SEEK_END);int b_fd = open(str_b,O_WRONLY);printf("%d",b_fd);printf("woshi:   %d",stdin);char buffer[BUFFER_SIZE];int read_cnt;while((read_cnt = read(a_fd,buffer,BUFFER_SIZE)) > 0){write(b_fd,buffer,read_cnt);}printf("bei bei");close(a_fd);close(b_fd);
}

2：库函数

#includevoid showdiff(char  *file1,char * file2, char *file3);// 反斜线是相对路径，正斜线是绝对路径
// 使用绝对路径int main(){printf("hello beibei\n");showdiff("C:\\Users\\jiang000\\CLionProjects\\helloWorld\\1.txt","C:\\Users\\jiang000\\CLionProjects\\helloWorld\\2.txt","C:\\Users\\jiang000\\CLionProjects\\helloWorld\\3.txt");//    showdiff("./1.txt",
//             "./2.txt",
//             "./3.txt");printf("hello ");
}void showdiff(char  *file1,char * file2, char *file3){FILE * fp1 = 0, *fp2 = 0, * fp3 = 0;char ch1,ch2;fp1 = fopen(file1,"r");fp2 = fopen(file2,"r");fp3 = fopen(file3,"w");while(1){// fp1ch1 = (char) fgetc(fp1);ch2 = (char) fgetc(fp2);if(feof(fp1) or feof(fp2)){break;}if(ch1 == ch2){printf("%c       \n",ch1);fputc(ch1,fp3);}}fclose(fp1);fclose(fp2);fclose(fp3);
}

3：相关知识

• #define stdin (__acrt_iob_func(0))
• #define stdout (__acrt_iob_func(1))
• #define stderr (__acrt_iob_func(2))

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