How do I concatenate two strings in C

Question

How do I add two strings   I tried name    derp     herp    but I got an error      Expression must have integral or enum type

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include  lt string h gt   include  lt stdio h gt  int main        int a l     char str 50  str1 50  str3 100      printf   nEnter a string         scanf   s  str      str3 0    0      printf   nEnter the string which you want to concat with string one         scanf   s  str1      strcat str3 str      strcat str3 str1      printf   nThe string is  s n  str3

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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  lt string h gt   include  lt stdio h gt    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

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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  lt stdlib h gt   include  lt string h gt   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

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In C  you don t really have strings  as a generic first-class object  You have to manage them as arrays of characters  which mean that you have to determine how you would like to manage your arrays  One way is to normal variables  e g  placed on the stack  Another way is to allocate them dynamically using malloc   Once you have that sorted  you can copy the content of one array to another  to concatenate two strings using strcpy or strcat   Having said that  C do have the concept of  string literals   which are strings known at compile time  When used  they will be a character array placed in read-only memory  It is  however  possible to concatenate two string literals by writing them next to each other  as in  foo   bar   which will create the string literal  foobar

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Concatenate Strings  Concatenating any two strings in C can be done in atleast 3 ways  -  1  By copying string 2 to the end of string 1   include  lt stdio h gt   include  lt string h gt   define MAX 100 int main       char str1 MAX  str2 MAX     int i j 0    printf  Input string 1        gets str1     printf   nInput string 2        gets str2     for i strlen str1  str2 j     0  i       Copying string 2 to the end of string 1          str1 i  str2 j        j          str1 i    0     printf   nConcatenated string        puts str1     return 0      2  By copying string 1 and string 2 to string 3   include  lt stdio h gt   include  lt string h gt   define MAX 100 int main       char str1 MAX  str2 MAX  str3 MAX     int i j 0 count 0    printf  Input string 1        gets str1     printf   nInput string 2        gets str2     for i 0 str1 i     0  i               Copying string 1 to string 3         str3 i  str1 i       count          for i count str2 j     0  i          Copying string 2 to the end of string 3         str3 i  str2 j       j          str3 i    0     printf   nConcatenated string         puts str3     return 0      3  By using strcat   function   include  lt stdio h gt   include  lt string h gt   define MAX 100 int main       char str1 MAX  str2 MAX     printf  Input string 1        gets str1     printf   nInput string 2        gets str2     strcat str1 str2                        strcat   function   printf   nConcatenated string         puts str1     return 0

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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  lt stdlib h gt           calloc  include  lt stdarg h gt           va    include  lt string h gt           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 lt count   i            len    strlen va arg ap  char         va end ap           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 lt count   i                  char  s   va arg ap  char            strcpy merged null pos  s           null pos    strlen s             va end ap        return merged      Usage   include  lt stdio h gt            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      Output        Empty line a ab abc   Clean-up  Note that you should free up the allocated memory when it becomes unneeded to avoid memory leaks   char  str   concat 2  a   b    println str   free str

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Without GNU extension    include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   int main void        const char str1      First       const char str2      Second       char  res       res   malloc strlen str1    strlen str2    1       if   res            fprintf stderr   malloc   failed  insufficient memory  n            return EXIT FAILURE             strcpy res  str1       strcat res  str2        printf  Result    s  n   res       free res       return EXIT SUCCESS      Alternatively with GNU extension    define  GNU SOURCE  include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   int main void        const char str1      First       const char str2      Second       char  res       if  -1    asprintf  amp res    s s   str1  str2             fprintf stderr   asprintf   failed  insufficient memory  n            return EXIT FAILURE             printf  Result    s  n   res       free res       return EXIT SUCCESS      See malloc  free and asprintf for more details

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include  lt stdio h gt   int main        char name       derp   herp       printf     s   n   name     derpherp      return 0

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You cannot add string literals like that in C  You have to create a buffer of size of string literal one   string literal two   a byte for null termination character and copy the corresponding literals to that buffer and also make sure that it is null terminated  Or you can use library functions like strcat

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You should use strcat  or better  strncat  Google it  the keyword is  concatenating

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using memcpy  char  str1  hello   char  str2   world   char  str3   str3  char    malloc  11  sizeof char    memcpy str3 str1 5   memcpy str3 strlen str1  str2 6    printf   s    s    s  str1 str2 str3   free str3

[c] How do I concatenate two strings in C?

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