So i have this problem in c++.
I open a file and read it char by char and print it on screen.
It works fine until I add this to the program.
gr=0; The complete program:
int main() { int gr; char *ch; gr=0;//this causes the problem FILE *fp; fp=fopen("as.txt","r"); do { *ch=fgetc(fp); cout<<*ch<<endl; } while (*ch!=EOF); } 
char *ch; *ch=fgetc(fp); You created a pointer, but you never actually made it point to anything.
That it appeared to work without the gr=0 assignment is pure chance, likely a result of various factors contributing to values in memory. When you dereference invalid pointers, sometimes you get a segmentation fault and othertimes you just silently overwrite some memory that's not yours, causing further bugs down the line.
I have no idea what you need a pointer for here, anyway. Surely simply declare a char ch and use that.
Your code seg faults on me. You might try something like the code listed below.
#include <cstdio> #include <iostream> int main() { FILE *fp; char c; fp=fopen("str.cpp","r"); if(fp != NULL) { do { c=fgetc(fp); std::cout << c << std::endl; } while (c!=EOF); } } The problem is in the char pointer.You never actually allocate memory for it it's just some random pointer thus giving you undefined behavior.This is why it worked without the gr on your machine but it's just random and it won't work in most cases.
What you want to do is allocate memory for it like that :
int main() { int gr; char *ch=new char; gr=0;//this has nothing to do with the problem FILE *fp; fp=fopen("as.txt","r"); do { *ch=fgetc(fp); cout<<*ch<<endl; } while (*ch!=EOF); delete ch; //For each new there must be a delete return 0; } 