I get a bus error in the following code

Question

I get a bus error in my code. With this code, I am trying to convert numbers to words, but I know there is a flaw in my logic. But before that, when I compile and run this code using g ++ on mac, I try to make this code as it is, and I get a bus error. Any help would be appreciated.

When I run the code, I get the following output. I have debug messages to keep track of where the error occurs.

  Enter a number: 1234
     main 1: numbers are: 234
     Function1: Number is 234
     two
     two hundred 
     34 Function2: Number is 34
     Function3: Number is 34
     Bus error: 10

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#include <iostream> #include <string> using namespace std; char *convert_number(int); char *tens[]={"","ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"}; char *words[]={"zero","one", "two", "three", "four", "five", "six", "seven", "eight", "nine","ten","eleven","twelve","thirteen","fourteen","fifteen","sixteen","seventeen", "eighteen","ninteen"}; char *place[]={"","hundred","thouands","million","billion","trillion"}; int main(int argc, char **argv) { int number,conv_num,places; places=1; char *string= new char[1000]; char *temp_string = new char[100]; cout<<"Enter a number:"; cin>>number; string=" "; if(number>=1000) { while(number>=1) { conv_num = number % 1000; cout<<"main 1:numbers are:"<<conv_num<<endl; temp_string=convert_number(conv_num); string =strcat(string,temp_string); string =strcat(string," "); number = 0;// (number-conv_num)/1000; cout<<"main 2:numbers are:"<<endl; //cout<<conv_num<<":"<<number<<endl; } } else { string = convert_number(number); string =strcat(string," "); } cout<<"Main: The word is :"<<string<<endl; } char *convert_number(int number) { int divisor; char *word; word = new char[100]; divisor=10; cout<<"Function1: Number is "<<number<<endl; if (number>=100) { word =strcat(word,words[number/100]); cout<<word<<endl; word =strcat(word," hundred "); cout<<word<<endl; number=number%100; cout<<number; } cout<<"Function2: Number is "<<number<<endl; if(number >=20) { word=strcat(word,tens[number/10]); word =strcat(word," "); if(number%divisor>=1) { word=strcat(word,words[number%divisor]); word =strcat(word," "); } } cout<<"Function3: Number is "<<number<<endl; if(number<20) { word=strcat(word,words[number]); word =strcat(word," "); } cout<<"Returning word:"<<word; return word; } 

Answer 1

The reason you get bus errors is because you are trying to write to a non-writable area (i.e., to a character constant, as well as beyond its end); this behavior is undefined.

 // Good: allocate 100 bytes to string char *string = new char[100]; // Bad! Compiler warns you that assigning character const to char* is wrong. // It does not tell you that you've just leaked the 100 bytes that you allocated /// before, but that also true. string=" "; // ... some more code, and then string = strcat(string,temp_string); // <<== HERE is the problem! 

The call to strcat tries to write string ending in zero, and then continues writing beyond the end of the line. This behavior is undefined, so your program crashes.

To fix this problem, you need to copy " " to string , and not assign it to the string pointer.