Concatenate four string constants into one

I have two string constants const char * like this:

const char * p1 = "abcd";
const char * p2 = "efgh";

I want to convert these into a single s开发者_高级运维tring so that it becomes a file name:

const char * filename = "abcd_efgh.txt";

I tried to concatenate the char * but failed. Kindly guide me as to how to do this.

Thanks

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char* are pointers, i.e they hold the address of the memory segment where the data is stored. You need to allocate a new, large enough buffer and then use the strcat() function to concatenate the strings.

This is really the C way to do this, not the C++ way. In C++ you should use a string class, such as std::string which handles all the buffer allocation stuff for you.

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I would go with sprintf()

char buffer[strlen(p1) + strlen(p2) + 6];
sprintf(buffer, "%s_%s.txt", abcd, efgh);

(You're adding 6 for the _, .txt, and the \0 to terminate the string; 1 + 4 + 1)

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You could use the strcat function:

/* strcat example */
#include <stdio.h>
#include <string.h>

int main ()
{
  char str[80];
  strcpy (str,"these ");
  strcat (str,"strings ");
  strcat (str,"are ");
  strcat (str,"concatenated.");
  puts (str);
  return 0;
}

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You have declared the filename string const, which is too restrictive for what you want to do at runtime, but can be done by the pre-processor at compile time, using the adjacent string rule:

#define PART1 "abcd"
#define PART2 "efgh"

const char* p1 = PART1 ;
const char* p2 = PART2 ;

const char* filename = PART1 "_" PART2 ".txt"

However if you don't need filename to be a const use one of the already proposed solutions.

---

const std::string p1 = "abcd";
const std::string p2 = "efgh";

std::string filename = p1 + "_" + p2 + ".txt";

---

Try this:

char name1[] = "my_demo";
char name2[] = "_file.txt";

char* filename = (char*) malloc(sizeof(char) * (strlen(name1) + strlen(name2) + 1));
strcpy(filename, name1);
strcat(filename, name2);

printf("Filename is: %s \n", filename);

free(filename);

Outputs:

Filename is: my_demo_file.txt