CODEWITHSUNDEEP
c
BradyUnger
BradyUnger

Reputation: 11

C language - removing uninitialized space in string

I have the following code:

char *string = malloc(strlen(stringa) + strlen(stringb) + 1);
strcpy(string, stringa);
strcpy(string+strlen(stringa), stringb);

the problem is, with what I'm doing, stringa is sometimes NULL, and when it is and it gets copied to string, it results in uninitialized characters at the very beginning of string. Here's an example of the output that I am getting when stringa happens to be NULL:

�����o
This is a test
To see the output
of string

I want to get rid of the characters at the beginning that are uninitialized. What I tried doing so far is:

memset(string, 0, strlen(string));

and

memset(string, 0, sizeof(string));

both have given me errors and do not solve my problem. Anyone know how I could edit 'string' to get rid of the uninitialized characters? This could either be applied to 'string' directly or to 'stringa' before it gets copied to 'string'.

Upvotes: 0

Views: 139

Answers (2)

Malcolm McLean
Malcolm McLean

Reputation: 6404

In very old C, on many platforms, a nul byte happened to be hardcoded to location zero in memory, and so there wasn't a distinction between the null string and the empty string. It's a bit of an odd difference if you think of it, no string of sausages versus a string of no sausages.

You can easily resurrect the old behaviour, by wrapping strcpy

char *strcpy_oldbehaviour(char *dest, const char *src)
{
   if(src)
     return strcpy(dest, src);
   else
     return strcpy(dest, "");
}

Upvotes: 0

Dov Benyomin Sohacheski
Dov Benyomin Sohacheski

Reputation: 7742

You can always run some logical tests with a conditional statement on the value of the strings before you begin copying them:

Option 1:

char*  string;
size_t length = 0;

if (stringa != NULL) {
    length += strlen(stringa);
}

if (stringb != NULL) {
    length += strlen(stringb);
}

string = malloc(length + 1);

// Copy the strings

Option 2:

char* string = NULL;

if (stringa != NULL) {
    string = malloc(strlen(stringa) + 1);
    strcpy(string, stringa);
}

if (stringb != NULL) {
    if (string != NULL) {
        string = realloc(string, strlen(stringb) + 1);
        strcat(string, stringb);
    } else {
        string = malloc(strlen(stringb) + 1);
        strcpy(string, stringb);
    }
}

Upvotes: 1

Related Questions