pointer to address using another pointer C

Question

I've got a function which receives a pointer to a string. Now I want to duplicate this pointer, so I could run on the string with one pointer, and have another pointer which saves the beginning of the string. I hope my question is clear, I don't want to create a pointer to the pointer (which points to where the first pointer points and changes with it), I want a pointer which will point to the address of which the first pointer points.

I tried many different ways but none of them worked, this is my latest try, I keep getting "initialization makes pointer from integer without a cast"

int move_chars (char *str, int start, int end, int dist){
    int strsize = end - start + 1;
    char *p =  *str;

char *p = str; as str is a char* and *str is a char. — hmjd
– hmjd, Commented Jan 18, 2013 at 15:24

Martín Valdés de León · Accepted Answer · 2013-01-18 15:29:52Z

7

Since p is of type char * and str is also of type char *, you just need to do:

char *p = str;

To make p point to the same memory location as str.

Your code:

char *p = *str;

Attempts to copy into p the value of the first char at the memory location that str points to, and since p is expecting another memory location and not a char, you get an error.

Your error says that "initialization makes pointer from integer without a cast". This is telling you what's happening: The compiler thinks you are manually pointing p to a specific memory location, using the value of the char *str returns as an integer. This is technically doable, but you are required to manually cast the integer into a pointer, just so it's clear you're doing what you intended, and it's not a bug like in your case.

edited Jan 18, 2013 at 15:29

answered Jan 18, 2013 at 15:24

Martín Valdés de León

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simonc · Accepted Answer · 2013-01-18 15:24:07Z

5

Use

char *p =  str;

to declare a pointer to a char and initialise it with the value of another char pointer.

answered Jan 18, 2013 at 15:24

simonc

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2 Comments

user1108310 Over a year ago

Thanks for your answer cant belive that I didnt try this! If I want to move the pointer forward should I use p++ or *p++? cant seem to find the diference//

simonc Over a year ago

Use p++ to move the pointer forward. *p++ could be used to combine assignment and pointer increment, often in a loop. e.g. while(*src != '\0') *dest++ = *src++; as a strcpy implementation.

Raghu Srikanth Reddy · Accepted Answer · 2013-01-18 15:43:14Z

1

char *p = str

This will declare a pointer to character and makes p point to the memory location where str points

answered Jan 18, 2013 at 15:43

Raghu Srikanth Reddy

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3 Comments

user1108310 Over a year ago

Thanks for your answer! but why when try to do *str=p rihgt after your suggested answer I get an error again?

Raghu Srikanth Reddy Over a year ago

@user1108310: what are you doing? it should be char *p = str;

user1108310 Over a year ago

first I do char *p =str, than p++ ,and now I want to bring str to where p points, so Im supposed to do *str=p right? but that doesnt work

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