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

#pragma warning(disable : 4996)

char* rtrim(char* s)
{
if(s == NULL)
return NULL;

// set tail white space as '\0'
for(size_t i = strlen(s)-1; i >= 0 && s[i] == ' '; i--)
s[i] = '\0';

return s;
}

char* ltrim(char* s)
{
if(s == NULL)
return NULL;

char* p;

// skip head white space
for(p = s; *p == ' '; p++)
;

if(p != s) // if address p is not same as address s
{
size_t length = strlen(p);

if(length > 0) // so p is not null
{
memmove(s, p, length);
s[length] = '\0';
}
}

return s;
}

char* trim(char* s)
{
if(s == NULL)
return NULL;

rtrim(s);

return ltrim(s);
}

int main()
{
char s[10];
strcpy(s, " ab cde ");

trim(s);

printf("after trim:\n");

if(*s != '\0')
printf("%s, length = %d\n", s, strlen(s));
else
printf("s is null\n");

return 0;
}
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