Linux C编程练习（一）

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本文介绍了自制ls命令实现及多种文件操作技巧，包括目录遍历、文件逆序输出及父子进程间的信号传递。

1、定制自己的ls命令

#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
#include <time.h>
void do_ls(char*dir_entry);
void do_ls_filename(char*dir_entry);
void do_stat( char* filename );
void show_list( char* filename, struct stat* statinfo );
void mode_to_letters( mode_t filemode, char str[] );
void show_time( time_t filetime );
char* format_time( char* dsttime, const char* srctime );

//用户id转名称
char* uid_to_name( uid_t uid );
//组id转名称
char* gid_to_name( gid_t gid );

int flag;
int main(int argc,char*argv[])
{
    char*dir=".";
    if(argc>2)
    {
        dir=argv[3];  
    }
    //printf("%s\n",dir );
    //printf("%c\n",argv[2][1] );
    switch(argv[2][1]){
        case 'l':flag=0;do_ls(argv[3]);break;
        case 'A':flag=1;do_ls(argv[3]);break;
        case 'n':flag=2;do_ls(argv[3]);break;
        case 'a':flag=3;do_ls(argv[3]);break;
        case 'm':flag=4;do_ls(argv[3]);break;
    }
}

void do_ls(char* dir_entry) {
    DIR* pDir;
    struct dirent* pCurDir;
    if( ( pDir = opendir( dir_entry ) ) == NULL ){
        perror( "read dir" );
        exit( -1 );
    }
    else {
        while( ( pCurDir = readdir( pDir ) ) != NULL ) {
            //printf("%s\n",pCurDir->d_name );
            do_stat( pCurDir->d_name );
        }
        closedir( pDir );
    }
}

//得到文件信息
void do_stat( char* filename ){
    struct stat statinfo;
    if ( stat( filename, &statinfo ) == -1 ) {
        printf( "打开%s失败\n", filename );
        exit( -1 );
    }else {

        show_list( filename, &statinfo );
    }
}

//显示文件列表
void show_list( char* filename, struct stat* statinfo ) {
    mode_t st_mode = statinfo->st_mode;

    char str[10];
    mode_to_letters( st_mode, str );
    switch(flag){
        case 0:{
            printf( "%s\t", str );                         //文件权限和文件类型信息
            printf( "%ld\t", statinfo->st_nlink ); //该文件上硬链接个数 
            printf( "%s\t\t", uid_to_name( statinfo->st_uid ) ); //UID号转用户名
            printf( "%s\t", gid_to_name( statinfo->st_gid ) ); //GID号转组名
            printf( "%10ld", statinfo->st_size ); //文件大小
            show_time( statinfo->st_mtime ); //最后一次修改时间
            printf( "\t%s", filename );

            printf( "\n" );
                };break;
        case 1:{
            printf("%s ",filename );   
        };break;
        case 2:{
            printf( "%s\t", str );                         //文件权限和文件类型信息
            printf( "%ld\t", statinfo->st_nlink ); //该文件上硬链接个数 
            printf( "%d\t\t", statinfo->st_uid  ); //UID号
            printf( "%d\t", statinfo->st_gid  ); //GID号
            printf( "%10ld", statinfo->st_size ); //文件大小
            show_time( statinfo->st_mtime ); //最后一次修改时间
            printf( "\t%s", filename );
            printf( "\n" );
        };break;
        case 3:
            printf("%s ", filename);break;
        case 4:
            printf("%s,",filename);break;
    }
    printf("\n");
}

char* uid_to_name( uid_t uid ){
    return getpwuid( uid )->pw_name;
}

char* gid_to_name( gid_t gid ){
    return getgrgid( gid )->gr_name;
}

void mode_to_letters( mode_t filemode, char str[] ) {

    strcpy( str, "----------" );
    if( S_ISREG( filemode ) ) str[0] = '-';
    if( S_ISDIR( filemode ) ) str[0] = 'd';
    if( S_ISLNK( filemode ) ) str[0] = 'l';

    //用户权限位
    if( filemode & S_IRUSR ) str[1] = 'r';
    if( filemode & S_IWUSR ) str[2] = 'w';
    if( filemode & S_IXUSR ) str[3] = 'x';

    //组权限位
    if( filemode & S_IRGRP ) str[4] = 'r';
    if( filemode & S_IWGRP ) str[5] = 'w';
    if( filemode & S_IXGRP ) str[6] = 'x';

    //其他组权限位
    if( filemode & S_IROTH ) str[7] = 'r';
    if( filemode & S_IWOTH ) str[8] = 'w';
    if( filemode & S_IXOTH ) str[9] = 'x';
}

void show_time( time_t filetime ) {
    struct tm* ptm;
    ptm = localtime( &filetime );

    int month = ptm->tm_mon + 1;
    int day = ptm->tm_mday;
    int hour = ptm->tm_hour;
    int min = ptm->tm_min;

    char srchour[3] = "0";
    char srcmin[3] = "0";
    char dsthour[3] = "0";
    char dstmin[3] = "0";
    sprintf( srchour, "%d", hour );
    sprintf( srcmin, "%d", min );
    format_time( dsthour, srchour );
    format_time( dstmin, srcmin );

    printf( "%4d月%4d%4s:%2s", month, day, dsthour, dstmin );
}

char* format_time( char* dsttime, const char* srctime ) {
    if( strlen( srctime ) < 2 ) {
        return strcat( dsttime, srctime );
    }
    return strcpy( dsttime, srctime );
}

运行结果：

#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <dirent.h>
#include <sys/stat.h>
#include <stdlib.h>
#define MAX 102
void printdir(char*dir,int depth)
{
    DIR *dp;
    struct dirent *entry;
    struct stat statbuf;

    if((dp=opendir(dir))==NULL)
    {

        //fprintf(stderr,"can't not open directory:%s\n",dir);
        return;
    }

    chdir(dir);
    while((entry=readdir(dp)) != NULL)
    {
        lstat(entry->d_name,&statbuf);
        if(S_ISDIR(statbuf.st_mode))
        {
            if(strcmp(".",entry->d_name)==0||strcmp("..",entry->d_name)==0)
                continue;
            printf("%*s%s/\n",depth,"",entry->d_name);
            printdir(entry->d_name,depth+4);
        }
        else 
            printf("%*s%s\n",depth,"",entry->d_name);
    }
    closedir(dp);
}


int main()
{
    char buffer[MAX];
    char *p=getcwd(buffer,MAX);
    printf("The current directory:%s\n",buffer);
    printdir(buffer,0);
    return 0;
}

3、对文本文件的内容进行逆序输出，要求按行，按词，同时按行和词逆序三种输出方式。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXSIZE 1024
struct node{
    char *line;
    struct node *next;
};


char* getWord(char word[]);
void read_line();
void read_word();
void read_mixture();


FILE *in, *out;
char buf[MAXSIZE];
int cnt;

int main(){
    char op;
    printf("请选择文件输出形式：\n");
    printf("1、按行逆序\n");
    printf("2、按词逆序\n");
    printf("3、混合逆序\n");
    printf("请输入你的选择(按q退出)：");
    while(scanf("%c",&op)&&op!='q')
    {
        switch(op){
        case '1':read_line();break;
        case '2':read_word();break;
        case '3':read_mixture();break;
        }
    }
    return 0;
}


void read_line()
{
    printf("\n");
    struct node *head = (struct node*)malloc(sizeof(struct node));

    if(NULL == (in = fopen("test.txt", "r"))){
        printf("Error while open the file\n");
        //return -1;
    }

    head->next = NULL;
    while(NULL != fgets(buf, MAXSIZE, in)){
        struct node *pnode = (struct node*)malloc(sizeof(struct node));
        pnode->line = (char*)malloc(strlen(buf));
        pnode->next = NULL;

        sprintf(pnode->line, "%s", buf);
        if(NULL != head->next){
            pnode->next = head->next;
            head->next = pnode;
        }
        else{
            head->next = pnode;
        }
    }

    while(NULL != head->next){
        struct node *pnode = head->next;
        fputs(pnode->line, stdout);
        head->next = pnode->next;
        free(pnode->line);
        free(pnode);
    }
    free(head);
}

void read_word()
{
    struct node *head = (struct node*)malloc(sizeof(struct node));
    if(NULL == (in = fopen("test.txt", "r"))){
        printf("Error while open the file\n");
        //return -1;
    }

    head->next = NULL;
    while(NULL != fgets(buf, MAXSIZE, in)){
        struct node *pnode = (struct node*)malloc(sizeof(struct node));
        pnode->line = (char*)malloc(strlen(buf));
        pnode->next = NULL;

        sprintf(pnode->line, "%s", buf);
    for(int i=strlen(pnode->line);i>=0;i--)
    {
        printf("%c",(pnode->line)[i]);
    }
        if(NULL != head->next){
            pnode->next = head->next;
            head->next = pnode;
        }
        else{
            head->next = pnode;
        }
    }
    fclose(in);
    printf("\n");
}

void read_mixture()
{
    struct node *head = (struct node*)malloc(sizeof(struct node));

    if(NULL == (in = fopen("test.txt", "r"))){
        printf("Error while open the file\n");
        //return -1;
    }

    head->next = NULL;
    while(NULL != fgets(buf, MAXSIZE, in)){
        struct node *pnode = (struct node*)malloc(sizeof(struct node));
        pnode->line = (char*)malloc(strlen(buf));
        pnode->next = NULL;

        sprintf(pnode->line, "%s", buf);
        if(NULL != head->next){
            pnode->next = head->next;
            head->next = pnode;
        }
        else{
            head->next = pnode;
        }
    }

    while(NULL != head->next){
        struct node *pnode = head->next;
        head->next = pnode->next;
    for(int i=strlen(pnode->line);i>=0;i--)
    {
        printf("%c",(pnode->line)[i]);
    }
        free(pnode->line);
        free(pnode);
    }
    free(head);
    printf("\n");
}

4、创建两个进程。父进程负责创建一个新的文本文件，并向文本文件中写入数据，当数据写入完成后，发送信号给子进程，子进程独处文件内容并显示。

#include<sys/types.h>
#include<unistd.h>
#include<stdio.h>
#include<fcntl.h>//perror()的头文件
#include<stdlib.h>
#include<string.h>
#include<signal.h>
#define MAXSIZE 1024
char buf[MAXSIZE];

int main(){
    //int fd=open("hello.txt",O_WRONLY);
    FILE *fp;
    int pid;
    char *hello="hello ";
    char *filename="hello.txt";
    if((fp=fopen(filename,"w+"))==NULL){
        perror("fopen");
        return -1;
    }
    if(fwrite(hello,strlen(hello),1,fp)<1)//fwrite返回成功写入文件的块数
            printf("fwrite hello error!\n");
    //printf("这是父进程\n");
    fclose(fp);
    pid=fork();
    if(pid==-1){//创建进程，失败返回-1
        perror("fork error");
        return -1;
    }
    if(pid==0){//子进程
        kill(getppid(),SIGALRM);
        fp=fopen("hello.txt","r");
        //printf("这是子进程\n");
        while(NULL != fgets(buf, MAXSIZE, fp)){
            fprintf(stdout,"%s\n",buf);
        }

    }
    //fclose(fp);
    return 0;
}