Concatenate two char strings in a C program

Question

I wrote the following C program   int main int argc  char   argv         char  str1      char  str2      str1    sssss       str2    kkkk       printf   s   strcat str1  str2         return  EXIT SUCCESS        I want to concatenate the two strings  but it doesn t work

User · Answer

When you use string literals  such as  this is a string  and in your case  sssss  and  kkkk   the compiler puts them in read-only memory  However  strcat attempts to write the second argument after the first  You can solve this problem by making a sufficiently sized destination buffer and write to that   char destination 10      5 times s  4 times k  one zero-terminator char  str1  char  str2  str1    sssss   str2    kkkk   strcpy destination  str1   printf   s  strcat destination str2      Note that in recent compilers  you usually get a warning for casting string literals to non-const character pointers

User · Answer

The way it works is to    Malloc memory large enough to hold copies of str1 and str2 Then it copies str1 into str3 Then it appends str2 onto the end of str3 When you re using str3 you d normally free it free  str3     Here s an example for you play with  It s very simple and has no hard-coded lengths  You can try it here  http   ideone com d3g1xs  See this post for information about size of char   include  lt stdio h gt   include  lt memory h gt   int main int argc  char   argv           char  str1        char  str2        str1    sssss         str2    kkkk         char   str3    char    malloc 1   strlen str1   strlen str2           strcpy str3  str1         strcat str3  str2         printf   s   str3          return 0

User · Answer

strcat str1  str2  appends str2 after str1  It requires str1 to have enough space to hold str2  In you code  str1 and str2 are all string constants  so it should not work  You may try this way   char str1 1024   char  str2    kkkk   strcpy str1   ssssss    strcat str1  str2   printf   s   str1

User · Answer

strcat  concats str2 onto str1  You ll get runtime errors because str1 is  not being properly allocated for concatenation

User · Answer

Here is a working solution    include  lt stdio h gt   include  lt string h gt   int main int argc  char   argv           char str1 16         char str2 16         strcpy str1   sssss          strcpy str2   kkkk          strcat str1  str2         printf   s   str1         return 0      Output   ssssskkkk   You have to allocate memory for your strings  In the above code  I declare str1 and str2 as character arrays containing 16 characters  I used strcpy to copy characters of string literals into them  and strcat to append the characters of str2 to the end of str1  Here is how these character arrays look like during the execution of the program   After declaration  both are empty    str1                                            str2                                            After calling strcpy   0 is the string terminator zero byte    str1   s  s  s  s  s   0                               str2   k  k  k  k   0                                 After calling strcat   str1   s  s  s  s  s  k  k  k  k   0                       str2   k  k  k  k   0

User · Answer

strcat attempts to append the second parameter to the first  This won t work since you are assigning implicitly sized constant strings   If all you want to do is print two strings out  printf   s s  str1 str2     Would do   You could do something like   char  str1   calloc sizeof  SSSS   sizeof  KKKK   1 sizeof  str1   strcpy str1  SSSS    strcat str1 str2     to create a concatenated string  however strongly consider using strncat strncpy instead  And read the man pages carefully for the above   oh and don t forget to free str1 at the end

[c] Concatenate two char* strings in a C program

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