Difference between these two pointer to char initialisations

Question

I know this has been answer before, but I can't find the question.
What are the differences between these two initialisations:

int main() 
{
    char* pch1;
    char* pch2;

    pch1 = (char*)malloc(sizeof(char) * 5);
    strcpy(pch1, "Text");

    pch2 = "Text";
}

One points to heap memory, the other to the static data segment of the prgoram — StoryTeller - Unslander Monica, Feb 20 '14 at 11:20

score 2 · Answer 1 · answered Feb 20 '14 at 11:23

There are three main differences here:

The first one copies the content of a string literal into dynamic memory, while the second one points to that literal directly.
Modifying pch1 string is legal; modifying pch2 string is illegal
You need to free pch1 to avoid memory leak.

For completeness, consider pch3 which is initialized like this:

char tmp[] = "Text";
char *pch3 = tmp;

This pch3 is modifiable like your pch1, but it does not need freeing, because the content of the string is copied into automatic memory.

score 2 · Accepted Answer · edited May 23 '17 at 12:03

2

First: don't cast the return value from malloc - it's a common source of errors. Do I cast the result of malloc?

pch1 = malloc(sizeof(char) * 5);

assigns a pointer to a dynamically allocated block of 5 bytes on the heap.

pch2 = "Text";

should ideally be avoided because it assigns a pointer to a string literal. String literals are read-only on most OSes and is also a common source of mistakes. If you do this you should make the pointer to const

const char * pch2 = "Text";

edited May 23 '17 at 12:03

Community

1
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answered Feb 20 '14 at 11:23

Sergey L.

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I haven't programmed that much in C, but everywhere I see that the return value from malloc it is cast. Can you tell me why this is wrong? – Adrian Feb 20 '14 at 11:26
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In C++ you have to cast, in C you should not. Explained in detail here: http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc – Sergey L. Feb 20 '14 at 11:27

qwr · Answer 3 · 2014-02-20T11:29:09.223

1

pch1 points to heap

you can modify it within bounderies

plus you have to free it

other points to static data segment you can not modify it

edited Feb 20 '14 at 11:29

answered Feb 20 '14 at 11:23

qwr

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score 0 · Answer 4 · answered Feb 20 '14 at 11:47

0

pch1 will use heap memory for storing your data
pch2 - using stack memory

answered Feb 20 '14 at 11:47

sankar suriya

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Difference between these two pointer to char initialisations

4 Answers4