Here we go again: when to use Malloc and when not?

**django** · 08-09-2011

What is OP?

**django** · 08-09-2011

Originally Posted by CommonTater

Code:

char *test = "This is a test";
strcpy(test,"And now it's over");

That is modifying a string literal and you can't do that. The reason you can't do that is that test is pointing to the read only section of the program's PE Image.

You are confusing me. In another thread where I was wrestling with trying to concatenate stuff, you posted this code where you do the same:

Originally Posted by CommonTater

Like this....

Code:

#include <stdio.h>
#include <string.h>

#define BEGIN "@@"
#define END "CCC"

int main (void)
  {  char *result = calloc(100,sizeof(char));  // create some string space

    strcat(result, BEGIN);                       // result holds @@
    strcat(result, "this is a message");     //  result holds @@this is a message
    strcat(result, END);                         // result holds @@this is a messageCCC

    printf("%s\n\n", result);
    free(result); 
    return 0; }

Alll so nice and simple...

Not to be annoying, but I just would like to understand what is not correct.

**whiteflags** · 08-09-2011

It's not the same thing in the slightest.

Name
strcat, strncat - concatenate two strings

Synopsis

#include <string.h>
char *strcat(char *dest, const char *src);
char *strncat(char *dest, const char *src, size_t n);

Description
The strcat() function appends the src string to the dest string overwriting the '\0' character at the end of dest, and then adds a terminating '\0' character. The strings may not overlap, and the dest string must have enough space for the result.

The strncat() function is similar, except that it will use at most n characters from src. Since the result is always terminated with '\0', at most n+1 characters are written.

Return Value
The strcat() and strncat() functions return a pointer to the resulting string dest.

Conforming to
SVr4, 4.3BSD, C89, C99.

Assigning "string" to some random pointer does not allocate memory to it. In fact, the pointer just points to a string you aren't really supposed to change, whether the computer let's you or not.

I do hope that people stop feeding you code though because of things like this.

**Salem** · 08-09-2011

> What is OP?
Original Poster (the thread starter)

**django** · 08-09-2011

Originally Posted by whiteflags

It's not the same thing in the slightest.

Assigning "string" to some random pointer does not allocate memory to it. In fact, the pointer just points to a string you aren't really supposed to change, whether the computer let's you or not.

I do hope that people stop feeding you code though because of things like this.

Darn, stupid, I see the difference now, thanks.

**~~CommonTater~~** · 08-09-2011

Originally Posted by django

You are confusing me. In another thread where I was wrestling with trying to concatenate stuff, you posted this code where you do the same:

Not the same at all... In my strcat example I am copying FROM string literals into a memory buffer... I am modifying the memory buffer, the string literals are never modified, only copied.

**django** · 08-09-2011

Got it, got it, I already had my .......... kicked

**~~CommonTater~~** · 08-09-2011

Originally Posted by django

Got it, got it, I already had my .......... kicked

Gee... and it only took 52 messages...

(Recent epidemic of people trying totally bizarre stuff, notwithstanding)

Thread: Here we go again: when to use Malloc and when not?

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