How to define one variable using another one in c?

Question

How to define a variable using another variable.Actually I want a whole string but that string should contain data from another variable.

#include <stdio.h>
char *Data1 = "23";
char *Data2 = "267";
char *Data = ("www.mywebsite.com?c=%s&v=%s", Data1, Data2);

int main() {
  printf(Data);
  return 0;
}

Please read the manual pages. Please read about the comma operator — Ed Heal
– Ed Heal, Commented Jan 15, 2017 at 8:22

Sourav Ghosh · Accepted Answer · 2017-01-15 08:26:22Z

3

You can define an array and make use of sprintf()/snprintf() to generate the final string.

Something like

char final[128] = {0};   //128 is arbitrary value

int data1 = 23;    //no need to be string for integer value
int data2 = 267;

snprintf(final, 128, "www.mywebsite.com?c=%d&v=%d", data1, data2);

That said, printf(Data); is very invalid. You either

use the proper format specifier, like printf("%s", final);
use puts(final);

edited Jan 15, 2017 at 8:26

answered Jan 15, 2017 at 8:20

Sourav Ghosh

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3 Comments

Valar_Dohaeris Over a year ago

how do i store the output of statment snprintf(final, 128, "www.mywebsite.com?c=%d&v=%d", data1, data2); in one variable.I want output as a whole string.

Sourav Ghosh Over a year ago

@bhagyakathole Did you read the linked manual page? It is stored into final.

Valar_Dohaeris Over a year ago

Is there any another solution for this statement snprintf(final, 128, "www.mywebsite.com?c=%d&v=%d", data1, data2);?my compiler is showing an error for this statement.

tdao · Accepted Answer · 2017-01-15 08:24:50Z

0

You can use snprintf

First define a MAX_LEN and a buffer

#define MAX_LEN 1000
char Data[MAX_LEN + 1] = "";

then use snprintf to fill in all strings:

snprintf( Data, sizeof(Data), "www.mywebsite.com?c=%s&v=%s", Data1, Data2);

edited Jan 15, 2017 at 8:24

answered Jan 15, 2017 at 8:22

tdao

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5 Comments

Sourav Ghosh Over a year ago

1) why MAX_LEN+1 ? 2) you missed passing the size.

tdao Over a year ago

@SouravGhosh about 1) it's called LEN, and so the size is +1

Sourav Ghosh Over a year ago

Sorry, but I still did not get. sprintf() writes at most n so why the extra byte needed?

DYZ Over a year ago

@SouravGhosh is right: "The functions snprintf() and vsnprintf() write at most size bytes (including the terminating null byte ('\0')) to str."

tdao Over a year ago

it's just how I call the name of the constant - nothing to do with the snprintf, usually MAX_LEN (strlen) doesn't include the NUL character, whereas MAX_SIZE (sizeof) does.

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