c - Pointer Content was deleted after function call, why? -

i've been trying figure out what's going on code, no luck. have defined pointer: char ** fileslist = readdir(); pointer pointing array of strings. able have filenames in current directory. that's not issue.

when pass fileslist[i], i=0,..,n : readimage(fileslist[i],...); content of fileslist erased.. don't know why.. help?!

my code:

#include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <syslog.h> #include <sys/stat.h> #include <time.h> #include <string.h> #include <unistd.h> #include <limits.h> #include <dirent.h>  #include <jpeglib.h>  unsigned char *readimage(//struct jpeg_decompress_struct cinfo,                          char *inputpath,                          int *width,                          int *height,                          int *pixel_size) {     char *inputfilename;     struct jpeg_decompress_struct cinfo;     unsigned char *buffer;     int rc, i, j;     struct stat file_info;     unsigned long jpg_size;     unsigned char *jpg_buffer;      struct jpeg_error_mgr jerr;     int row_stride;      inputfilename = (char *)malloc(1 + strlen(inputpath));     strcpy(inputfilename, inputpath);      rc = stat(inputfilename, &file_info);     if (rc) {         syslog(log_err, "failed stat source jpg");         exit(exit_failure);     }     jpg_size = file_info.st_size;     jpg_buffer = (unsigned char*) malloc(jpg_size + 100);      int fd = open(inputfilename, o_rdonly);     = 0;     while (i < jpg_size) {         rc = read(fd, jpg_buffer + i, jpg_size - i);         += rc;     }     close(fd);      cinfo.err = jpeg_std_error(&jerr);      jpeg_create_decompress(&cinfo); // <-- @ point, inputpath's content erased ...      jpeg_mem_src(&cinfo, jpg_buffer, jpg_size);      rc = jpeg_read_header(&cinfo, true);      if (rc != 1) {         syslog(log_err, "file not seem normal jpeg");         exit(exit_failure);     }      jpeg_start_decompress(&cinfo);     *width = cinfo.output_width;     *height = cinfo.output_height;     *pixel_size = cinfo.output_components;      unsigned long bmp_size = cinfo.output_width * cinfo.output_height * cinfo.output_components;     buffer = (unsigned char*)malloc(bmp_size);      row_stride = cinfo.output_width * cinfo.output_components;      while (cinfo.output_scanline < cinfo.output_height) {         unsigned char *buffer_array[1];         buffer_array[0] = buffer + (cinfo.output_scanline) * row_stride;          jpeg_read_scanlines(&cinfo, buffer_array, 1);     }      jpeg_finish_decompress(&cinfo);     jpeg_destroy_decompress(&cinfo);     free(jpg_buffer);      return buffer; }  char **readdir(int *nof) {     char **fileslist;     int numfiles = 0;     int size = 256;     dir *d;     struct dirent *dir;      d = opendir(".");     if (d) {         fileslist = (char **)malloc(size);         while ((dir = readdir(d)) != null) {             if (strstr(dir->d_name, ".jpeg")) {                 printf("%s\n", dir->d_name);                 fileslist[numfiles] = (char *)malloc(256);                 fileslist[numfiles++] = dir->d_name;                 size += 256;                 fileslist = realloc(fileslist, size);             }         }         closedir(d);     }     *nof = numfiles;     return fileslist; }  int main(int argc, char *argv[]) {     unsigned char *buffer;     char **fileslist;     int numberoffiles;     int width;     int height;     int pixel_size;     int i;      fileslist = readdir(&numberoffiles);      (i = 0; < numberoffiles; ++i) {         printf("file: %s\n", fileslist[i]); // <-- here prints nothing in second round          buffer = readimage(fileslist[i],                            &width,                            &height,                            &pixel_size);     }     //free(temp);     free(fileslist);      return exit_success; } 

check this:

 jpeg_create_decompress(&cinfo); // <-- @ point, inputpath's content erased ...  // after point, filenames erased 

if want run code, download library jpeglib 8c then, export folder's path path & c_include_path then, compile with:

gcc file.c -ljpeg 

the directory enumeration function incorrect:

• you allocate memory directory entry, instead of copying string that, overwrite pointer allocated dir->d_name, contents may clobbered further readdir calls.
• your allocation scheme imprecise , fail long filenames.

here corrected version:

char **readdir(int *nof) {     char **fileslist = null;     int numfiles = 0;     dir *d;     struct dirent *dir;      d = opendir(".");     if (d) {         while ((dir = readdir(d)) != null) {             if (strstr(dir->d_name, ".jpeg")) {                 printf("%s\n", dir->d_name);                 fileslist = realloc(fileslist, (numfiles + 1) * sizeof(char*));                 fileslist[numfiles++] = strdup(dir->d_name);             }         }         closedir(d);     }     *nof = numfiles;     return fileslist; } 

note readdir() should take path argument, , strstr not precise way match fie extensions: list.jpeg.txt mistakenly included in list.