What is the meaning of Bus: error 10 in C

Question

Below is my code

#import <stdio.h>
#import <string.h>

int main(int argc, const char *argv[])
{
    char *str = "First string";
    char *str2 = "Second string";
    
    strcpy(str, str2);
    return 0;
}

It compiles just fine without any warning or errors, but when I run the code I get the error below

Bus error: 10

What did I miss ?

Answer 1

For one, you can't modify string literals. It's undefined behavior.

To fix that you can make str a local array:

char str[] = "First string";

Now, you will have a second problem, is that str isn't large enough to hold str2 . So you will need to increase the length of it. Otherwise, you will overrun str - which is also undefined behavior.

To get around this second problem, you either need to make str at least as long as str2 . Or allocate it dynamically:

char *str2 = "Second string";
char *str = malloc(strlen(str2) + 1);  //  Allocate memory
//  Maybe check for NULL.

strcpy(str, str2);

//  Always remember to free it.
free(str);

There are other more elegant ways to do this involving VLAs (in C99) and stack allocation, but I won't go into those as their use is somewhat questionable.

---

As @SangeethSaravanaraj pointed out in the comments, everyone missed the #import . It should be #include :

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

Answer 2

There is no space allocated for the strings. use array (or) pointers with malloc() and free()

Other than that

#import <stdio.h>
#import <string.h>

should be

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

NOTE:

• anything that is malloc() ed must be free() 'ed
• you need to allocate n + 1 bytes for a string which is of length n (the last byte is for \\0 )

Please you the following code as a reference

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

int main(int argc, char *argv[])
{
    //char *str1 = "First string";
    char *str1 = "First string is a big string";
    char *str2 = NULL;

    if ((str2 = (char *) malloc(sizeof(char) * strlen(str1) + 1)) == NULL) {
        printf("unable to allocate memory \n");
        return -1; 
    }   

    strcpy(str2, str1);

    printf("str1 : %s \n", str1);
    printf("str2 : %s \n", str2);

    free(str2);
    return 0;
}

Answer 3

str2 is pointing to a statically allocated constant character array. You can't write to it/over it. You need to dynamically allocate space via the *alloc family of functions.

Answer 4

字符串文字在 C 中是不可修改的

Answer 5

Your code attempts to overwrite a string literal. This is undefined behaviour.

There are several ways to fix this:

1. use malloc() then strcpy() then free() ;
2. turn str into an array and use strcpy() ;
3. use strdup() .

Answer 6

this is because str is pointing to a string literal means a constant string ...but you are trying to modify it by copying . Note : if it would have been an error due to memory allocation it would have been given segmentation fault at the run time .But this error is coming due to constant string modification or you can go through the below for more details abt bus error :

Bus errors are rare nowadays on x86 and occur when your processor cannot even attempt the memory access requested, typically:

• using a processor instruction with an address that does not satisfy its alignment requirements.

Segmentation faults occur when accessing memory which does not belong to your process, they are very common and are typically the result of:

• using a pointer to something that was deallocated.
• using an uninitialized hence bogus pointer.
• using a null pointer.
• overflowing a buffer.

To be more precise this is not manipulating the pointer itself that will cause issues, it's accessing the memory it points to (dereferencing).

Answer 7

Whenever you are using pointer variables ( the asterix ) such as

char *str = "First string";

you need to asign memory to it

str = malloc(strlen(*str))

Answer 8

Let me explain why you do you got this error "Bus error: 10"

char *str1 = "First string";
// for this statement the memory will be allocated into the CODE/TEXT segment which is READ-ONLY

char *str2 = "Second string";
// for this statement the memory will be allocated into the CODE/TEXT segment which is READ-ONLY

strcpy(str1, str2);
// This function will copy the content from str2 into str1, this is not possible because you are try to perform READ WRITE operation inside the READ-ONLY segment.Which was the root cause 

If you want to perform string manipulation use automatic variables(STACK segment) or dynamic variables(HEAP segment)

Vasanth