How do I concatenate two strings in C?

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How do I add two strings?

I tried name = "derp" + "herp";, but I got an error:

Expression must have integral or enum type

C does not have the support for strings that some other languages have. A string in C is just a pointer to an array of char that is terminated by the first null character. There is no string concatenation operator in C.

Use strcat to concatenate two strings. You could use the following function to do it:

#include <stdlib.h>
#include <string.h>

char* concat(const char *s1, const char *s2)
    char *result = malloc(strlen(s1) + strlen(s2) + 1); // +1 for the null-terminator
    // in real code you would check for errors in malloc here
    strcpy(result, s1);
    strcat(result, s2);
    return result;

This is not the fastest way to do this, but you shouldn't be worrying about that now. Note that the function returns a block of heap allocated memory to the caller and passes on ownership of that memory. It is the responsibility of the caller to free the memory when it is no longer needed.

Call the function like this:

char* s = concat("derp", "herp");
// do things with s
free(s); // deallocate the string

If you did happen to be bothered by performance then you would want to avoid repeatedly scanning the input buffers looking for the null-terminator.

char* concat(const char *s1, const char *s2)
    const size_t len1 = strlen(s1);
    const size_t len2 = strlen(s2);
    char *result = malloc(len1 + len2 + 1); // +1 for the null-terminator
    // in real code you would check for errors in malloc here
    memcpy(result, s1, len1);
    memcpy(result + len1, s2, len2 + 1); // +1 to copy the null-terminator
    return result;

If you are planning to do a lot of work with strings then you may be better off using a different language that has first class support for strings.

String concatenation in C, In this C programming example, you will learn to concatenate two strings manually without using the strcat() function. Program to Concatenate Two Strings Using Pointer Functions. This program for string concatenation in c is the same as above. However, this time we are passing pointers to Functions to separate the logic from the main program.

#include <stdio.h>

int main(){
    char name[] =  "derp" "herp";
    printf("\"%s\"\n", name);//"derpherp"
    return 0;

C Program to Concatenate Two Strings, Method 2: Using append() function. Syntax: string& string::append (const string& str) str: the string to be appended. Here str is the object of std::string class which  In C, "strings" are just plain char arrays. Therefore, you can't directly concatenate them with other "strings". You can use the strcat function, which appends the string pointed to by src to the end of the string pointed to by dest: char *strcat(char *dest, const char *src); Here is an example from

David Heffernan explained the issue in his answer, and I wrote the improved code. See below.

A generic function

We can write a useful variadic function to concatenate any number of strings:

#include <stdlib.h>       // calloc
#include <stdarg.h>       // va_*
#include <string.h>       // strlen, strcpy

char* concat(int count, ...)
    va_list ap;
    int i;

    // Find required length to store merged string
    int len = 1; // room for NULL
    va_start(ap, count);
    for(i=0 ; i<count ; i++)
        len += strlen(va_arg(ap, char*));

    // Allocate memory to concat strings
    char *merged = calloc(sizeof(char),len);
    int null_pos = 0;

    // Actually concatenate strings
    va_start(ap, count);
    for(i=0 ; i<count ; i++)
        char *s = va_arg(ap, char*);
        strcpy(merged+null_pos, s);
        null_pos += strlen(s);

    return merged;
#include <stdio.h>        // printf

void println(char *line)
    printf("%s\n", line);

int main(int argc, char* argv[])
    char *str;

    str = concat(0);             println(str); free(str);
    str = concat(1,"a");         println(str); free(str);
    str = concat(2,"a","b");     println(str); free(str);
    str = concat(3,"a","b","c"); println(str); free(str);

    return 0;


  // Empty line

Note that you should free up the allocated memory when it becomes unneeded to avoid memory leaks:

char *str = concat(2,"a","b");

Methods to concatenate string in C/C++ with Examples , In the C Programming Language, the strcat function appends a copy of the string " "); /* Concatenate the following two strings to the end of  To understand this example, you should have the knowledge of the following C programming topics: As you know, the best way to concatenate two strings in C programming is by using the strcat () function. However, in this example, we will concatenate two strings manually. Here, the strings s1 and s2 and concatenated and the result is stored in

You should use strcat, or better, strncat. Google it (the keyword is "concatenating").

C Language: strcat function (String Concatenation), In the following program user would be asked to enter two strings and then the program would concatenate them. For concatenation we have not used the. C program to concatenate two strings, for example, if the two input strings are "C programming," and " language" (note the space before language), then the output will be "C programming language." To concatenate the strings, we use strcat function of string.h, to concatenate without using the library function, see another program below.

I'll assume you need it for one-off things. I'll assume you're a PC developer.

Use the Stack, Luke. Use it everywhere. Don't use malloc / free for small allocations, ever.

#include <string.h>
#include <stdio.h>

#define STR_SIZE 10000

int main()
  char s1[] = "oppa";
  char s2[] = "gangnam";
  char s3[] = "style";

    char result[STR_SIZE] = {0};
    snprintf(result, sizeof(result), "%s %s %s", s1, s2, s3);
    printf("%s\n", result);

If 10 KB per string won't be enough, add a zero to the size and don't bother, - they'll release their stack memory at the end of the scopes anyway.

C Program to concatenate two strings without using strcat, Appends a NULL character to the destination string when all characters of the source string are copied to the destination string. Here is an example: 1. 2. 3. 4. Concatenation of two strings is simple copying a string to another. To concatenate two strings str1 and str2, you will copy all characters of str2 at the end of str1. Below is the step by step descriptive logic to concatenate two string. Input two string from user. Store it in some variable say str1 and str2. Here we need to concatenate str2 to

String Concatenation - How to play with strings in C, String concatenation in C program : In this article, We will show you, How to write a C program to Concatenate Two Strings without using strcat function. How to concatenate multiple strings (C# Guide) 02/20/2018; 3 minutes to read +2; In this article. Concatenation is the process of appending one string to the end of another string. You concatenate strings by using the + operator. For string literals and string constants, concatenation occurs at compile time; no run-time concatenation occurs.

C program to Concatenate Two Strings without using strcat(), Concatenation of two strings is the process of joining them together to form a new string. Concatenation appends the second string after first string  This program is used to concatenate two given strings as a single set of strings using the function strcat(). So first of all, you have to include the stdio header file using the "include" preceding # which tells that the header file needs to be process before compilation, hence named preprocessor directive.

C program to concatenate two strings, Default Methods in C++ with Examples; Taking String input with space in C (3 Different Methods) Print all distinct characters of a string in order (3 Methods) Count consonants in a string (Iterative and recursive methods) C Program to concatenate two strings without using strcat; How to concatenate two integer arrays without using loop in C

  • Small bit: code could do the copy of the first part of the string last and then return memcpy(result, s1, len1);. Although a micro-optimization or at least a bit of code golfing, such potential improvements on basic string operations can have value given their high use.
  • It also works for macros in c, which is worth noting
  • The arguments to calloc are backward. They should be count then size. You get away with it here thanks to the multiplicative identity, since sizeof(char) is defined to be 1.
  • Consider int len --> size_t len as size_t is the right type for "size" code. Also // room for NULL --> // room for null character NULL implies the null pointer.
  • Beware: strncat() is a fiendishly difficult function to use correctly. Quickly, without looking at the manual, what length do you specify to strncat()? If you said "the length of the buffer", you just demonstrated my point nicely. It has a counter-intuitive interface and when you have enough data to use it safely, you don't need to use the function in the first place — there are other, quicker and more efficient alternatives (such as strcpy() or memmove()) that could be used instead. Pretty much whatever the question of 'what should I use', strncat() is not the answer.
  • This would be more clearly expressed as snprintf(result, sizeof result, "%s %s %s", s1, s2, s3);