Manipulating Char Pointer - Topic

ROM

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Posts: 27,177

Joined: Mar 27 2008

Gold: 445.00

Apr 9 2017 06:54am

I have this:

Code

char * p = (char *)&mmemory[x];
printf("%x", p);

which outputs

Code

bf8fed34

How would I go about getting two 'strings' into variables to output this

Code

printf("%s,p1);
printf("\n%s,p2);

Code

bf8f
ed34

This post was edited by ROM on Apr 9 2017 06:55am

carteblanche

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Apr 9 2017 08:48am

not a c expert. off-hand, i think sprintf will give you a string instead of printing to console. then you can use whatever c's substring is to separate the digits.

ROM

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Posts: 27,177

Joined: Mar 27 2008

Gold: 445.00

Apr 10 2017 09:12pm

Quote (carteblanche @ Apr 9 2017 10:48am)

not a c expert. off-hand, i think sprintf will give you a string instead of printing to console. then you can use whatever c's substring is to separate the digits.

Thanks for the tip. =)
Here is my solution. Don't mind the cryptic variables names. It could be cleaned up a fair bit but finally got it.

Code

char * p = (char *)&mmemory[x];
char pa[MAX_BUFFER];
sprintf(pa,"%x",p);
printf("\n\n%s",pa);
int len = strlen(pa);
int len1 = len/2;
int len2 = len - len1;
char *s1 = malloc(len1+1); // one for the null terminator
memcpy(s1, pa, len1);
s1[len1] = '\0';
char *s2 = malloc(len2+1); // one for the null terminator
memcpy(s2, pa+len1, len2);
s2[len2] = '\0';
printf("\ns1=%s",s1);
printf("\ns2=%s\n\n",s2);

This post was edited by ROM on Apr 10 2017 09:12pm

ASBands

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Apr 16 2017 11:58am

You don't need to do all that copying if you embrace crazy string formatting.

Code

#include <cstdio>

int main()
{
// this is whatever you want to look at
const char some_buffer[] = "blah blah blah";

// Need extra +1 because snprintf thinks we care about null-termination
char ptr_str[sizeof(void*) * 2 + 1];

// The "%016x" format string left-pads with zeros, which is how people usually want to look at
// pointers. The annoying use a ternary operator to work on 32- and 64-bit machines (there is
// no standard macro for doing this, although SIZEOF_VOID_P works in every Linux distro).
snprintf(ptr_str, sizeof ptr_str, sizeof(void*) == 8 ? "%016x" : "%08x", some_buffer);

// The %.*s bit is a strange output-conversion bit which says to print exactly N characters.
printf("a=%.*s\n", sizeof ptr_str / 2, ptr_str);
printf("b=%.*s\n", sizeof ptr_str / 2, ptr_str + sizeof ptr_str / 2);
}

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