Concatenate cstrings c++

Question

When I run this, I get no errors, but the string does not get concatenated. Could someone tell me what I'm getting wrong here.

char *con(const char str[], int n) {
    char * t = new char[60];
    int l = strlen(str);
    t[l] = '\0';
    if (n <= 0) {
        return t;
    } else {
        for (int i = 0; i < n; i++) {
            strcat(t, str);
        }
        return t;
    }
}

If I try and take out the:

int l = strlen(str);
t[l] = '\0';

Then the program crashes.

There's a reason [`std::string`](http://en.cppreference.com/w/cpp/string/basic_string) was invented. — David G, Mar 16 '13 at 18:19
What is `s`? I don't see it defined anywhere. Is it null-terminated? — antonijn, Mar 16 '13 at 18:20
Really, do yourself a favor and either 1) replace the C++ tag with the C tag, or 2) use `std::string` and enjoy writing C++ — Andy Prowl, Mar 16 '13 at 18:21
@Antonijn n is the number of times the string should be concatenated — user12074577, Mar 16 '13 at 18:28
the `60` in your code seems a bit arbitrary, wouldn't it be better to calculate the buffer `t` with the help of `n` and `strlen(str)`? — AndersK, Mar 16 '13 at 18:38

score 1 · Accepted Answer · answered Mar 16 '13 at 18:23

1

You have to start with an empty string.

Replace:

int l = strlen(str);
t[l] = '\0';

With:

t[0] = '\0';

Now str will be concatenated n times in t.

The original code was leaving the first l-1 chars in t uninitialized.

answered Mar 16 '13 at 18:23

Christian Garbin

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hmm that didnt fix it, the program returns nothing if I call ("hi",5) – user12074577 Mar 16 '13 at 18:29

Concatenate cstrings c++

1 Answers1