#include <iostream>
using namespace std;
int main() {
char *s;
printf("enter a word \n");
scanf("%s", s);
int i;
for (i = 0; s[i] != '\0'; i++) {
}
printf("length is = %d", i);
return 0;
}
When I compile this program, a segmentation fault occurs.
Can anyone plz tell me, what is the problem in this code?
char *s;
Is unitialized, you can't assign an input stream to it until it is.
char s[100]; //space for 99 characters plus null terminator
or
char* s = malloc(100); //each char has the size of one byte
These are C tools, for C++, however, you can/should use std::string, with std::cin instead of scanf.
std::string s;
std::cin >> s;
If you must use C tools, scanf("%s", s); is not the most safe method, if you don't pass the size of the char array container, changing specifier %s to %100s or changing it altogether to a safer function like fgets(s, sizeof(s), stdin); is a better option.
scanf and tries to use std::string there, without resizing the string before, the same problem would exist. So it should be mentioned that if you use std::string you should also consider to switch to std::cin >>
%ns with a width (e.g. %100s) is a thing so can technically be done, but should probably mention. Also playing with macro's (or worse variables) to insert the right size in the format string isn't going to be pretty.char *s;
You created a pointer, though it does not point to anything (it is uninitialized).
scanf("%s",s);
You try to read data into the string pointed-to by s, but no such thing exists.
💥!
Allocate some memory and have s point to it… or, better yet, use std::string and std::cin.
char *s; printf("enter a word \n"); scanf("%s",s);
scanf with %s does not allocate memory, instead it reads into the buffer you provide it (e.g. s = malloc(100);. How big does that buffer need to be to avoid a buffer overflow? Unfortunately it can be however long until a whitespace character, so is inherently unsafe.
You can specify a max up front (not including null terminator!), but to handle variable size you then need to dynamically build the format string which gets complicated. As does what to do if the user enters a string too long.
char s[100];
scanf("%99s", s);
Since you tagged C++, you can use std::string and IO streams (e.g. std::cin for console input) which will handle all the memory allocation for you.
std::string s;
std::cout << "enter a word" << std::endl;
std::cin >> s;
In the case of C, you might use fgets(str, num, stream), this lets you specify the max length and avoid overflow in a simple manner.
char s[128];
fgetsf(s, 100, stdin);
Or with the POSIX 2008 scanf it can allocate the memory, but I don't believe this is universally supported, e.g. by Microsoft Visual Studio.
char *s = 0;
scanf("%ms", &s); // pass a pointer to a pointer!
free(s); // needs to be freed later!
chars in the memory locations pointed to bys. Where doesspoint?s. With that said if this isc++why are usingchar *, scanf(), andprintf()it's much simpler and less error prone if you use modernc++instead ofccode compiled in ac++compiler.printfis defined bycstdio