fopen - C programming - Open file with variable name -

i have lot of folders, , in each folder there lot of files, sequence of folders , files starts 0 till 100 etc.. i'm trying open each file using loop read what's in file, i'm getting error file pointer null. please help

for(int folder=0; folder<100; folder++) {      if(flag == 1)         break;      for(int file=filenumber; file<=filenumber; file++) {                char address[100] = {'\0'};         sprintf(address,"/volumes/partition 2/data structure/tags/%d/%d.txt",folder,filenumber);         files=fopen(address,"r");         if(files == null) {              printf("error opening file!\n");             flag = 1;             break;         }     }  } 

gwyn evans has answer pegged in comments, give him credit if provides answer, have 2 issues:

• you're starting second loop filenumber, instead of 0; and

• you not writing correct filename address, since you're using filenumber when should using file.

the following modification of algorithm should work you, in absence of problems in rest of absolute path you're using:

#include <stdio.h>  int main(void) {     int filenumber = 4;      (int folder = 0; folder < 2; folder++) {         (int file = 0; file < filenumber; file++) {             char address[100] = {'\0'};              sprintf(address, "%d/%d.txt", folder, file);             printf("trying open file %s...\n", address);              file * files = fopen(address, "r");             if (files == null) {                 perror("couldn't open file");             } else {                 printf("successfully opened file %s\n", address);                 fclose(files);             }         }     }     return 0; } 

which outputs:

paul@macbook:~/documents/src/scratch/fop$ ls 0       1       fopen   fopen.c paul@macbook:~/documents/src/scratch/fop$ ls 0 0.txt 1.txt 3.txt paul@macbook:~/documents/src/scratch/fop$ ls 1 0.txt 1.txt 3.txt paul@macbook:~/documents/src/scratch/fop$ ./fopen trying open file 0/0.txt... opened file 0/0.txt trying open file 0/1.txt... opened file 0/1.txt trying open file 0/2.txt... couldn't open file: no such file or directory trying open file 0/3.txt... opened file 0/3.txt trying open file 1/0.txt... opened file 1/0.txt trying open file 1/1.txt... opened file 1/1.txt trying open file 1/2.txt... couldn't open file: no such file or directory trying open file 1/3.txt... opened file 1/3.txt paul@macbook:~/documents/src/scratch/fop$  

moral of story: if things aren't working, trying printf()ing address check files you're actually trying open.