[Solved] String Functions: Strcat()

Question

You have a number of not just quite right beginning to each of your functions. Firstly, let’s think about the returns for each. myStrlen should return size_t instead of int. C++ designates a size_type for counters, measuring, etc.. The remaining functions should return char* (or nullptr on failure).

Looking at your myStrlen function where you have

for (i=0; str1[i] != '\0'; i++)
str1[i] = '\0';

You are setting every character in str1 to the nul-character because you are applying the loop to the next expression. You should not be worrying about nul-terminating anything within myStrlen — you are just counting characters. So you can rewrite it as follows:

size_t myStrlen (const char *str)
{
    size_t l = 0;
    for (; str[l]; l++) {}
    return l;
}

Your myStrcpy looks workable, though you should always validate your input parameters are not nullptr before using them — I leave that to you. Since you have a myStrlen function, you can simply use that along with memcpy to create your myStrcpy function as:

char *myStrcpy (char *dest, const char *src)
{
    size_t len = myStrlen(src);
    return (char *)memcpy (dest, src, len + 1);
}

(note: traditionally you have source (src) and destination (dest) parameters when copying or concatenating)

For your myStrcat function, you are just using the myStrlen function to find the offset in dest to append src, so you really just need a call to myStrlen and then a call to myStrcpy to copy src to that offset in dest, e.g.

char *myStrcat (char *dest, const char *src)
{
    size_t len = myStrlen (dest);
    return myStrcpy (dest + len, src);
}

In your main(), if you want a space between "Hello" and "World", then const int SIZE = 11; is one too-low to hold the concatenated string "Hello World" which would require 12-bytes (including the nul-terminating character). Do Not Skimp on buffer size. 128 is plenty small.

Remaining with your main() but updating SIZE = 12; and adding a space between "Hello" and "World" with an additional call to myStrcat, you could do the following:

int main (void)
{
    const int SIZE = 12;    /* too short by 1 if you add space between */
    char s1[SIZE] = "Hello";
    char s2[SIZE] = "World";

    std::cout << "s1: " << " " << s1 << std::endl << std::endl;
    std::cout << "The length of s1: " << myStrlen(s1) << std::endl << std::endl;

    std::cout << "Doing strcat(s1, s2) " << std::endl;
    myStrcat(s1, " ");
    myStrcat(s1, s2);
    std::cout << "s1: " << " " << s1 << std::endl;
    std::cout << "The length of s1: " << myStrlen(s1) << std::endl << std::endl;

    std::cout << "Doing strcpy(s1, s2) " << std::endl;
    myStrcpy(s1, s2);
    std::cout << "s1: " << " " << s1 << std::endl;
    std::cout << "The length of s1: " << myStrlen(s1) << std::endl << std::endl;
}

(note: don’t include using namespace std;, it is just bad form in this day and age)

Example Use/Output

$./bin/mystrcpy
s1:  Hello

The length of s1: 5

Doing strcat(s1, s2)
s1:  Hello World
The length of s1: 11

Doing strcpy(s1, s2)
s1:  World
The length of s1: 5

Look things over and let me know if you have further questions.

Accepted Answer