C函数，打印到缓冲区

Question

I have a client/ server application, and i get an error there -> perror ("[server] Can't send the message to client.\\n"). So the server cant' send the msgrasp ( the buffer). If you can help, I'll be grateful.

void printdir(char *dir, int depth)
{
    DIR *dp;
    struct dirent *entry;
    struct stat statbuf;
    if((dp = opendir(dir)) == NULL) {
        fprintf(stderr,"cannot open directory: %s\n", dir);
        return;
    }
    chdir(dir);
    while((entry = readdir(dp)) != NULL) {
        lstat(entry->d_name,&statbuf);
        if(S_ISDIR(statbuf.st_mode)) {
            /* Found a directory, but ignore . and .. */
            if(strcmp(".",entry->d_name) == 0 ||
                strcmp("..",entry->d_name) == 0)
                continue;
            printf("%*s%s/\n",depth,"",entry->d_name);
            /* Recurse at a new indent level */
            printdir(entry->d_name,depth+4);
        }
        else printf("%*s%s\n",depth,"",entry->d_name);
    }
    chdir("..");
    closedir(dp);
}

int printForClient(int fd)
{
  char buffer[100];
  int bytes;
  char msg[100];
  char *msgrasp=NULL;

  bytes = read (fd, msg, sizeof (buffer));
  if (bytes < 0)
    {
      perror ("Can't read from client.\n");
      return 0;
    }
  printf ("[server]..%s\n", msg);
  printdir(&msgrasp,msj,0);    
  printf("[server]%s\n",msgrasp);

  if (bytes && write (fd, msgrasp, bytes) < 0)
    {
      perror ("[server] Can't send the message to client.\n");
      return 0;
    }

  return bytes;
}

Answer 1

I would suggest adding an argument of type char* (a pointer to a char array) and at every recursion advance the pointer. My try (supposing the buffer is long enough for the output):

void printdir(char *dir, int depth, char* output)
{
    DIR *dp;
    struct dirent *entry;
    struct stat statbuf;
    char tmp[100];
    if((dp = opendir(dir)) == NULL) {
        fprintf(stderr,"cannot open directory: %s\n", dir);
        return;
    }
    chdir(dir);
    while((entry = readdir(dp)) != NULL) {
        lstat(entry->d_name,&statbuf);
        if(S_ISDIR(statbuf.st_mode)) {
            /* Found a directory, but ignore . and .. */
            if(strcmp(".",entry->d_name) == 0 ||
                strcmp("..",entry->d_name) == 0)
                continue;
            sprintf(tmp, "%*s%s/\n",depth,"",entry->d_name);
            strcpy(buffer, tmp);
            /* Recurse at a new indent level */
            printdir(entry->d_name,depth+4, buffer+strlen(tmp));
        }
        else printf("%*s%s\n",depth,"",entry->d_name);
    }
    chdir("..");
    closedir(dp);
}

int main()
{   char buffer[1000]; //buffer for printdir output.
    printf("Directory scan of /home:\n");
    printdir("/home",0);
    printf("done.\n");

    exit(0);
}

You might want to add \\n between every execution, depending on what you wish to do with the output. Please note that in this program \\0 at the end of each string is deleted.

Answer 2

This is not a very good Idea, but since it's what you requested here you have a solution with dynamic memory allocation

#include <stdio.h>
#include <dirent.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>

void printdir(char **output, const char *const dir, int depth)
{
    DIR *dp;
    struct dirent *entry;
    struct stat statbuf;

    if ((dp = opendir(dir)) == NULL)
    {
        fprintf(stderr,"cannot open directory: %s\n", dir);
        return;
    }
    chdir(dir);

    while ((entry = readdir(dp)) != NULL)
    {
        /* check if stat succeeded */
        if (lstat(entry->d_name, &statbuf) == -1)
            continue;
        if (S_ISDIR(statbuf.st_mode) != 0)
        {
            char *buffer;
            size_t length;

            /* Found a directory, but ignore . and .. */
            if(strcmp(".",entry->d_name) == 0 ||
                strcmp("..",entry->d_name) == 0)
                continue;
            length = 4 + depth + strlen(entry->d_name);
            if (*output != NULL)
                length += strlen(*output);
            buffer = realloc(*output, length);
            if (buffer != NULL)
            {
                char current[length];

                if (*output == NULL)
                    buffer[0] = '\0';
                *output = buffer;

                snprintf(current, length, "%*s%s/\n", depth, " ", entry->d_name);
                strcat(*output, current);
                //printf("%*s%s/\n",depth,"",entry->d_name);
                /* Recurse at a new indent level */
            }
            else
            {
                fprintf(stderr, "Out of memory\n");

                free(*output);
                *output = NULL;

                closedir(dp);
                return;
            }
            printdir(output, entry->d_name, depth + 4);
        }
        else
        {
            char  *buffer;
            size_t length;

            length = 4 + depth + strlen(entry->d_name);
            if (*output != NULL)
                length += strlen(*output);
            buffer = realloc(*output, length);
            if (buffer != NULL)
            {
                char current[length];

                if (*output == NULL)
                    buffer[0] = '\0';
                *output = buffer;

                snprintf(current, length, "%*s%s/\n", depth, " ", entry->d_name);
                strcat(*output, current);
            }
            else
            {
                fprintf(stderr, "Out of memory\n");

                free(*output);
                *output = NULL;

                closedir(dp);
                return;
            }
        }
    }
    chdir("..");

    closedir(dp);
}

int main()
{
    char *buffer = NULL; //buffer for printdir output.

    printf("Directory scan of /home:\n");
    printdir(&buffer, "/home", 0);
    printf("done.\n");

    printf("%s\n", buffer);
    free(buffer);

    exit(0);
}

It is not a very good Idea because you don't know if there will be enough memory to hold all the text, it could grow a lot, I added checks for that situation in this code, in the event of going out of memory, this function will abort reading, release resources and return.