Thread: Segmentation Fault

Hi need help. I can't understand why my program keeps on getting "Segmentation Fault". The last time I checked (in UBUNTU) it was already working, now I'm testing it in Windows and I keep on getting "Segmentation Fault".

Code:

#include <stdio.h>
#include <string.h>
     
 
int main(){
char string[1500];
char word[100];
int i,x,y,keyword=0,operator=0,s=0;
char *result;
char delims[] = "  \n";
char *keywords[] = {"auto", "break", "else", "case", "char", "const", "continue", "default", "do", "double",             "enum","extern","float","for","goto","if","int","long","register","return","short","signed",
        "sizeof","static","struct","switch","typedef","union","unsigned","void","volatile","while",
        "_Bool","_Complex","_Imaginary","inline","restrict","NULL"};
char *operators[]={"+", "-", "*", "/", "%","=","+=", "-=", "*=", "/=", "%=", "&=", "|=", "^=", "<<=", ">>=",
        "~", "&", "|", "^" ,"<<", ">>" ,"!", "&&", "||","?:", "==", "!=","( )","++", "--",".", "->",
        "<", "<=", ">", ">=", "*", "[ ]",",","(typename)","NULL"};
        


    printf("Enter Paragraph which can include spaces and Any number of lines.\n");
    printf("To terminate  press TAB and Enter.\n");
    scanf("%[^\t]",string);
    
    //Count the number of lines
    for(i=0;string[i]!='\0';++i) { 
    if (string[i]=='\n') ++s; } 
    printf("\nNo. of lines: %d\n",s); 
    
    //Tokenies paragraph
    strcpy(word, result);
    result = strtok( string, delims );
        while( result != NULL ) {
    strcpy(word, result);
    
    //Count number of keywords
        for( x = 0; keywords[ x ] != "NULL"; x++ ){   
        if ( strcmp ( word, keywords[x]) == 0 )
            keyword++;
        }
        
    //Count number of operators
        for( y = 0; operators[ y ] != "NULL"; y++ ){   
        if ( strcmp ( word, operators[y]) == 0 )
            operator++;
        }
           
    result = strtok( NULL, delims );
    }
    printf( "No. of keywords: %d.\n", keyword );
    printf( "No. of operators: %d.\n", operator );
}

Originally Posted by vart

line 30 - result is not initialized

Set it to NULL since it's an unused pointer.

The main point to make here is that you should turn up your compiler warning level. For gcc, try
gcc -Wall -Wextra yourprog.c

So can you explain why did this work??? because I can't figure out why. And I guess it's not because "result" was not initialized

Code:

#include <stdio.h>
#include <string.h>
     
 
int main(){
char string[1500];
char word[10];
int i,x,y,keyword=0,operator=0,s=0;
char *result;
char delims[] = "  \n";
char *keywords[] = {"auto", "break", "else", "case", "char", "const", "continue", "default", "do", "double","enum","extern","float","for","goto","if","int","long","register","return","short","signed",
        "sizeof","static","struct","switch","typedef","union","unsigned","void","volatile","while",
        "_Bool","_Complex","_Imaginary","inline","restrict","NULL"};
/*char *operators[]={"+", "-", "*", "/", "%","=","+=", "-=", "*=", "/=", "%=", "&=", "|=", "^=", "<<=", ">>=",
        "~", "&", "|", "^" ,"<<", ">>" ,"!", "&&", "||","?:", "==", "!=","( )","++", "--",".", "->",
        "<", "<=", ">", ">=", "*", "[ ]",",","(typename)","NULL"};*/
        


    printf("Enter Paragraph which can include spaces and Any number of lines.\n");
    printf("To terminate  press TAB and Enter.\n");
    scanf("%[^\t]",string);
    
    //Count the number of lines
    for(i=0;string[i]!='\0';++i) { 
    if (string[i]=='\n') ++s; } 
    printf("\nNo. of lines: %d\n",s); 
    
    //Tokenies paragraph
    strcpy(word, result);
    result = strtok( string, delims );
        while( result != NULL ) {
    strcpy(word, result);
    
    //Count number of keywords
        for( x = 0; keywords[ x ] != "NULL"; x++ ){   
        if ( strcmp ( word, keywords[x]) == 0 )
            keyword++;
        }
        
/*    //Count number of operators
        for( y = 0; operators[ y ] != "NULL"; y++ ){   
        if ( strcmp ( word, operators[y]) == 0 )
            operator++;
        }*/
           
    result = strtok( NULL, delims );
    }
    printf( "No. of keywords: %d.\n", keyword );
    printf( "No. of operators: %d.\n", operator );
}

Obviously it's possible for that line not to crash, but it's still a glaring error. Remove it and instead do
word[0] = '\0';

Also, comparing to the string literal "NULL" will only work if string literals are pooled.
It's more usual to use NULL, not "NULL".
Try removing the quotes from around all your NULL's.

Thank you to all of you, it worked! You guys are very helpful. I learned a lot today.

So can you explain why did this work???

Plain dumb luck. Look at these warnings my compiler spits out.

||=== c_homework, Debug ===|
main.c||In function ‘main’:|
main.c|36|warning: comparison with string literal results in unspecified behavior [-Waddress]|
main.c|8|warning: unused variable ‘y’ [-Wunused-variable]|
main.c|30|warning: ‘result’ is used uninitialized in this function [-Wuninitialized]|
||=== Build finished: 0 errors, 3 warnings (0 minutes, 5 seconds) ===|

That's the thing about undefined behavior, your program may appear to work today but tomorrow who knows.

If your not getting these warnings you need to increase your compiler warning levels.

By the way the undefined behavior is using the uninitialized pointer in the strcpy(). Why are you calling this function at this place (line 30) in your program?

Jim