How to create a new char* in standard C - c

Question

I have this code made for C++ (it works):
char* ConcatCharToCharArray(char *Str, char Chr)
{
char *StrResult = new char[strlen(Str) + 2];
strcpy(StrResult, Str);
StrResult[strlen(Str)] = Chr;
StrResult[strlen(Str) + 1] = '\0';
return StrResult;
}
/* Example: String = "Hello worl"
Char = "d"
Final string = "Hello world" */
The little problem is that I'm making a standard C program in Ubuntu and I need this code.
And "new" is NOT being recognized as a reserved word and there's even a red mark under it.
I tried: char *StrResult[strlen(Str) + 2], but it doesn't work because that way only admits constant values. I'm guessing "malloc" would be the standard C solution in here, how could I do this with "malloc" or any other way for that matter? Thank you so much.

Answer 1

new is the C++ way of allocating memory. In C you're right, you need to use malloc.
char* ConcatCharToCharArray(char *Str, char Chr)
{
size_t len = strlen( Str );
char *StrResult = malloc( len + 2 );
/* Check for StrResult==NULL here */
strcpy(StrResult, Str);
StrResult[len] = Chr;
StrResult[len+1] = '\0';
return StrResult;
}
When you're done with the memory, you'd call free( StrResult ).

Answer 2

Yes, you need malloc and you are confusing C with C++ here (since new comes from C++):
char *StrResult = (*char) malloc((strlen(Str) + 2) * sizeof(char));
char takes only one byte (see this question), so you don't need to multiply by it's size:
char *StrResult = (*char) malloc(strlen(Str) + 2);

Answer 3

One way:
char* ConcatCharToCharArray(char *Str, char Chr)
{
size_t StrLen = strlen(Str);
char *StrResult = malloc(StrLen + 2);
if(NULL == StrResult)
goto CLEANUP;
strcpy(StrResult, Str);
StrResult[StrLen++] = Chr;
StrResult[StrLen] = '\0';
CLEANUP:
return StrResult;
}
However, the above allocates a new string, instead of concatenating a character to an existing string. Here is a way to expand an existing string with an additional character:
int StrConcatChar(char **string, char character)
{
int rCode=0;
size_t stringLen;
char *temp;
if(NULL == string)
{
rCode=EINVAL;
goto CLEANUP;
}
stringLen = *string ? strlen(*string) : 0;
errno=0;
temp=realloc(*string, stringLen+2);
if(NULL == temp)
{
rCode=errno?errno:ENOMEM;
goto CLEANUP;
}
*string=temp;
(*string)[stringLen++] = character;
(*string)[stringLen] = '\0';
CLEANUP:
return(rCode);
}
The above function might be called like this:
{
int rCode=0;
char *buffer=NULL;
buffer=strdup("Hello worl");
if(NULL == buffer)
/* handle error condition */
rCode=StrConcatChar(&buffer, 'd');
if(rCode)
/* handle error condition */
...
if(buffer)
free(buffer);
}