How to add a char int to an char array in C

Question

How can I add     to the char Array     Hello World  in C  so I get a char Array   Hello World   The Question seems simple but I m struggling   Tried the following   char str 1024   char tmp         strcat str  tmp     But it does not work  It shows me the error   passing argument 2 of    strcat    makes pointer from integer without a cast  I know that in C a char can be cast as int aswell  Do I have to convert the tmp to an char array aswell or is there a better solution

User · Answer

The error is due the fact that you are passing a wrong to strcat(). Look at strcat()'s prototype:

   char *strcat(char *dest, const char *src);

But you pass char as the second argument, which is obviously wrong.

Use snprintf() instead.

char str[1024] = "Hello World";
char tmp = '.';
size_t len = strlen(str);

snprintf(str + len, sizeof str - len, "%c", tmp);

As commented by OP:

That was just a example with Hello World to describe the Problem. It must be empty as first in my real program. Program will fill it later. The problem just contains to add a char/int to an char Array

In that case, snprintf() can handle it easily to "append" integer types to a char buffer too. The advantage of snprintf() is that it's more flexible to concatenate various types of data into a char buffer.

For example to concatenate a string, char and an int:

char str[1024];
ch tmp = '.';
int i = 5;

// Fill str here

snprintf(str + len, sizeof str - len, "%c%d", str, tmp, i);

User · Answer

I think you ve forgotten initialize your string  str   You need initialize the string before using strcat  And also you need that tmp were a string  not a single char  Try change this   char str 1024      Only declares size char tmp          for  char str 1024     Hello World      Now you have  Hello World  in str char tmp 2

User · Answer

In C C   a string is an array of char terminated with a NULL byte    0        Your string str has not been initialized  You must concatenate strings and you are trying to concatenate a single char  without the null byte so it s not a string  to a string    The code should look like this   char str 1024     Hello World     this will add all characters and a NULL byte to the array char tmp 2           this is a string with the dot  strcat str  tmp      here you concatenate the two strings   Note that you can assign a string literal to an array only during its declaration  For example the following code is not permitted   char str 1024   str    Hello World     FORBIDDEN   and should be replaced with  char str 1024   strcpy str   Hello World      here you copy  Hello World  inside the src array

User · Answer

strcat has the declaration   char  strcat char  dest  const char  src    It expects 2 strings  While this compiles   char str 1024     Hello World   char tmp         strcat str  tmp     It will cause bad memory issues because strcat is looking for a null terminated cstring  You can do this   char str 1024     Hello World   char tmp 2          strcat str  tmp     Live example   If you really want to append a char you will need to make your own function  Something like this   void append char  s  char c            int len   strlen s           s len    c          s len 1      0      append str  tmp    Of course you may also want to check your string size etc to make it memory safe

User · Answer

Suggest replacing this   char str 1024   char tmp         strcat str  tmp     with this   char str 1024       0       set array to initial all NUL bytes char tmp             create a string for the call to strcat    strcat str  tmp

[c] How to add a char/int to an char array in C?

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