CODEWITHSUNDEEP
clinux
Morpheus
Morpheus

Reputation: 3

I am getting a SegFault error, but why?

I am getting a Segmentation Fault error when I run the code, but other than that it compiles and runs. If you know why the error is occurring, I'd appreciate the help. Also please explain why it is occurring, as I'm curious.

#include <stdio.h>
#include <string.h>
#include <stdbool.h>

int main()
{
    float att,def,hp,agi,stl,wis,ran,acc;
    char name[10],contents[100];
    int warrior,lvl=1,kills=0;

    printf("What is your name?\n");
    gets(name);

    printf("1: Ninja\n");
    printf("2: Knight\n");
    printf("3: Archer\n\n");
    printf("Pick a warrior.\n");
    scanf("%i",warrior);

    ...

    char attack[10],defense[10],health[10],agility[10],stealth[10],wisdom[10],range[10],accuracy[10],level[10],kill[10];
    snprintf(attack,10,"%f",att);
    snprintf(defense,10,"%f",def);
    snprintf(health,10,"%f",hp);
    snprintf(agility,10,"%f",agi);
    snprintf(stealth,10,"%f",stl);
    snprintf(wisdom,10,"%f",wis);
    snprintf(range,10,"%f",ran);
    snprintf(accuracy,10,"%f",acc);
    snprintf(level,10,"%f",lvl);
    snprintf(kill,10,"%f",kills);   

    char my_path[25];
    strcat(my_path,"Warriors/");
    strcat(my_path,name);
    strcat(my_path,".txt");


    FILE *fp;
    fp = fopen(my_path, "w+");

    fputs(attack, fp);
    fputs(" ", fp);
    fputs(defense, fp);
    fputs(" ", fp);
    fputs(health, fp);
    fputs(" ", fp);
    fputs(agility, fp);
    fputs(" ", fp);
    fputs(stealth, fp);
    fputs(" ", fp);
    fputs(wisdom, fp);
    fputs(" ", fp);
    fputs(range, fp);
    fputs(" ", fp);
    fputs(accuracy, fp);
    fputs(" ", fp);
    fputs(level, fp);
    fputs(" ", fp);
    fputs(kill, fp);

    fclose(fp);
}

Upvotes: 0

Views: 77

Answers (4)

user3629249
user3629249

Reputation: 16540

these two lines:

char my_path[25];
strcat(my_path,"Warriors/");

are incorrect because the strcat() function appends to the end of the current string (where it finds a NUL char '\0')

There is no telling where that NUL char will be found.

Suggest using:

char my_path[25];
strcpy(my_path,"Warriors/");

Upvotes: 0

sps
sps

Reputation: 2720

There are following issues in the code.

  1. Incorrect use of scanf while reading value for warrior.

    /* scanf("%i",warrior); */ // Put '&' before warrior
scanf("%i",&warrior);

  2. Incorrect format specifiers in snprintf while printing values of integers lvl, and kills. 

    /* snprintf(level,10,"%f",lvl); */ // Change %f to %d
snprintf(level,10,"%d",lvl);
/* snprintf(kill,10,"%f",kills); */ // Change %f to %d
snprintf(kill,10,"%d",kills);

  3. Using strcat with my_path without initializing it.

    /* char my_path[25]; */ // Initialize as seen below 
char my_path[25] = ""; 
strcat(my_path,"Warriors_");
strcat(my_path,name);
strcat(my_path,".txt");

  4. Finally, you are using gets, which should be avoided. You can change it to fgets.

Now coming to why your program is crashing.

First when you did scanf("%i",warrior);: Instead of the address (i.e. &warrior) you gave the value of warrior variable. And since warrior was not initialized, it had an indeterminate value. Now scanf treated the value of warrior as an address and tried to write the value there. And, since the value of warrior was indeterminate, it invoked undefined behavior.

Second when you used %f instead of %d (mismatch of format specifier) in snprintf, the code again invoked undefined behavior.

Third, when you use strcat without initializing my_path, your array my_path will have indeterminate values. Now, strcat looks for value 0 starting from the address pointed by my_path and keeps on looking untill it finds a 0. While doing this it may try to read value outside the array, again invoking undefined behavior.

When undefined behavior is invoked, anything can happen. In your case you got a segmentation fault.

P.S.: You should also check return value of scanf to check if it succeded or not.

P.S.: You should also check return value of fopen to check if it succeded or not.

Upvotes: 2

peter__barnes
peter__barnes

Reputation: 351

you'd better also add this kind of code to check if fopen is successful.

  if(fp==NULL)
  {   
      printf("can't open file:%s\n",my_path);
  }   
  else
  {
      ......
  }

Upvotes: 0

lost_in_the_source
lost_in_the_source

Reputation: 11237

scanf("%i",warrior);

scanf expects a pointer. http://linux.die.net/man/3/scanf

Fix it to

scanf("%i", &warrior);

Upvotes: 1

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