Thread: String concatenation

Whenever I deem possible, and after completing a given exercise from the two books I'm using to learn C++, I try to do the same thing but this time with pointers, arrays, c-style strings, and lots, lots, of consts.

I do this to try to consolidate my knowledge of these err... illusive constructs. However, I get this pervading feeling I could do it in a simpler way while still using the C style code. Maybe I can blame my Visual Basic background, and it's overly high-level nature, for this...

This is one of those moments. The following function is my solution to one of the exercises found on C++ Primer 4th Edition. Basically, a minimalist solution to output the plural of a word.

I would like you to comment on two things, if possible:

1. Did I complicate things unecessarily by using strncpy() and strncat()? Is there a simpler solution?

2. The dnamic c-string was the only way I found to be able to produce an array that can obviously only know its size at run-time. Had I choose not to create it dynamically, but instead fixed, would there be another solution other than passing the size of both strings as arguments to the function?

Code:

const char* plural(const char* word, const char* pls = "s") {
    char* ret = new char[strlen(word) + strlen(pls) + 1];
    strncpy(ret, word, strlen(word) + 1);
    strncat(ret, pls, strlen(pls) + 1);
    return ret;
}

'new' is C++, not C. Look up functions such as malloc and free. Don't cast them, because C doesn't need it. That's another C++ thing.

Default arguments are also C++. If you're really trying to learn C++, then post in the appropriate forum. If you're posting C, post here, but not in C++.

C99 supports arrays whose length is determined at runtime. Most compilers are not fully C99 compliant however, but will offer such extensions.


Quzah.

If some moderator sees this, could you please move to the C++ forum?

Wouldn't strcat() and strcpy() still force me to pass the string dimensions to the function? Or are you refering to question 1?

EDIT: (And aren't they unsafer solutions?)

My solution here is to use snprintf(), but you will have to #include <cstdio>.

PHP Code:

int length = snprintf(NULL, 0, "%s%s", word, pls); 
// snprintf() returns how many items it would have put in the string if it were big enough, 
// so we call it with NULL and 0 first.
char * ret = new char[length];
snprintf(ret, length, "%s%s", word, pls); 


That looks about right. It's one of the safest solutions because there is always enough space for both strings in the destination buffer and it is guaranteed to be null terminated. This is not the case with string functions sometimes, if you use them badly.