How to concatenate strings in an output function?

Question

Some languages have easy ways of doing this, but my question revolves in C and C++.

I wanna do something like this in Java:

public class sandbox {
    public static void main(String[] args) {
        System.out.println("Thank" + " you!");
    }
}

And transfer it in C:

#include <stdio.h>

int main() {
    /* The easiest way is like this:
        char *text1 = "Thank";
        char *text2 = " you";
        printf("%s%s\n", text1, text2);
    */
    printf("Thank" + " you."); // What I really want to do
}

How do I concatenate strings in a language like this?

Why not use `std::string` when you have tagged this question as C++ as well? That supports string concatenation. — Rohan Bari, Sep 13 '20 at 08:52
Nothing is wrong with the commented part, I want to know how to concatenate strings the usual way. — , Sep 13 '20 at 08:52
The answer is different if we are either talking about C or C++ — Roberto Caboni, Sep 13 '20 at 08:56
The answer for C is `strcat` (or `strncat` function) but it requires the knowledge about what a string is and how it is stored in memory. Basically a string is a nul-terminated array of chars, and the destination buffer of the concatenation must have enough room for the new string. There's no automatic reallocation in C. — Roberto Caboni, Sep 13 '20 at 09:00
Is this question already answered here? https://stackoverflow.com/questions/8465006/how-do-i-concatenate-two-strings-in-c — Kevin Boone, Sep 13 '20 at 10:22

score 2 · Accepted Answer · edited Sep 13 '20 at 09:05

2

You use just nothing:

puts ("Thank" " you.");

edited Sep 13 '20 at 09:05

Roberto Caboni

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answered Sep 13 '20 at 08:52

Christopher Yeleighton

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1

If the strings were literals in general I'm pretty sure this question would not have been asked... – Peter Sep 13 '20 at 08:53
1

Yes -- this is the degenerate case. – Kevin Boone Sep 13 '20 at 10:15

armagedescu · Answer 2 · 2020-09-13T09:00:28.360

1

This is a concatenation, but is a constant or compile time concatenation, you can't concatenate strings like that, but in case you need to split a string constant in multiple parts is ok:

...
    printf("Thank"  " you."); // What I really want to do
...

For dynamic, runtime concatenation you need strcat like

strcat(text1, text2);

First you must assure that you have enough memory in target string, see this link http://www.cplusplus.com/reference/cstring/strcat/
Ok, that was the C way, but C++ has STL with std::string

#include <iostream>
#include <string>
using namespace std;
int main()
{
    string str1 = "hello ", str2 = "world";
    cout<< str1 + str2<< endl;
    return 0;
}

edited Sep 13 '20 at 09:00

answered Sep 13 '20 at 08:54

armagedescu

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If you are only printing then you don't need the + in c++, just use <<. – kelalaka Sep 13 '20 at 09:31
@kelalaka it is about concatenation – armagedescu Mar 15 '22 at 14:53
It is a costly operation that construct a new string object then print output. – kelalaka Mar 15 '22 at 18:22
@kelalaka It is about how to use concatenation. – armagedescu Mar 17 '22 at 13:52

Shovo · Answer 3 · 2020-09-13T09:00:07.963

What I have understood from your question, hope the below solution will answer your question.

#include <stdio.h>

int main() {
  char s1[100] = "Thank ", s2[] = "You";
  int length, j;

  // store length of s1 in the length variable
  length = 0;
  while (s1[length] != '\0') {
    ++length;
  }

  // concatenate s2 to s1
  for (j = 0; s2[j] != '\0'; ++j, ++length) {
    s1[length] = s2[j];
  }

  // terminating the s1 string
  s1[length] = '\0';

  printf("After concatenation: %s",s1);


  return 0;
}

In C++, you can easily concatenate two string it by adding two string with a + operator.

#include <iostream>
using namespace std;

int main()
{
    string s1, s2, result;

    cout << "Enter string s1: ";
    cin>>s1;

    cout << "Enter string s2: ";
    cin>>s2;

    result = s1 + s2;

    cout << "After concatenation: = "<< result;

    return 0;
}

score 1 · Answer 4 · answered Sep 13 '20 at 08:57

Concatenating strings is not that easy in C unfortunately, here's how to do it most succinctly:

char *text1 = "Thank";
char *text2 = " you";

char *text_concat = malloc(strlen(text1) + strlen(text2) + 1);
assert(text_concat);

text_concat = strcpy(text_concat, text1);
text_concat = strcat(text_concat, text2);

printf("%s\n", text_concat);

free(text_concat);

score 0 · Answer 5 · answered Sep 13 '20 at 15:16

0

It is not possible in C to do something like printf("Thank" + " you."); because C doesn't support Operator Overloading Unlike C++. You can refer Is it possible to overload operators in C?

answered Sep 13 '20 at 15:16

Wasit Shafi

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How to concatenate strings in an output function?

5 Answers5