Briefly:
I'm after the equivalent of .NET's String.Trim in C using the win32 and standard C api (compiling with MSVC2008 so I have access to all the C++ stuff if needed, but I am just trying to trim a char*).
Given that there is strchr, strtok, and all manner of other string functions, surely there should be a trim function, or one that can be repurposed...
Thanks
void ltrim(char str[PATH_MAX])
{
int i = 0, j = 0;
char buf[PATH_MAX];
strcpy(buf, str);
for(;str[i] == ' ';i++);
for(;str[i] != '\0';i++,j++)
buf[j] = str[i];
buf[j] = '\0';
strcpy(str, buf);
}
void inPlaceStrTrim(char* str) {
int k = 0;
int i = 0;
for (i=0; str[i] != '\0';) {
if (isspace(str[i])) {
// we have got a space...
k = i;
for (int j=i; j<strlen(str)-1; j++) {
str[j] = str[j+1];
}
str[strlen(str)-1] = '\0';
i = k; // start the loop again where we ended..
} else {
i++;
}
}
}
Surprised to see such implementations. I usually do trim like this:
char *trim(char *s) {
char *ptr;
if (!s)
return NULL; // handle NULL string
if (!*s)
return s; // handle empty string
for (ptr = s + strlen(s) - 1; (ptr >= s) && isspace(*ptr); --ptr);
ptr[1] = '\0';
return s;
}
It is fast and reliable - serves me many years.
/* Function to remove white spaces on both sides of a string i.e trim */
void trim (char *s)
{
int i;
while (isspace (*s)) s++; // skip left side white spaces
for (i = strlen (s) - 1; (isspace (s[i])); i--) ; // skip right side white spaces
s[i + 1] = '\0';
printf ("%s\n", s);
}
This made me want to write my own - I didn't like the ones that had been provided. Seems to me there should be 3 functions.
char *ltrim(char *s)
{
while(isspace(*s)) s++;
return s;
}
char *rtrim(char *s)
{
char* back = s + strlen(s);
while(isspace(*--back));
*(back+1) = '\0';
return s;
}
char *trim(char *s)
{
return rtrim(ltrim(s));
}
You can use the standard isspace() function in ctype.h to achieve this. Simply compare the beginning and end characters of your character array until both ends no longer have spaces.
"spaces" include:
' ' (0x20) space (SPC)
'\t' (0x09) horizontal tab (TAB)
'\n' (0x0a) newline (LF)
'\v' (0x0b) vertical tab (VT)
'\f' (0x0c) feed (FF)
'\r' (0x0d) carriage return (CR)
although there is no function which will do all of the work for you, you will have to roll your own solution to compare each side of the given character array repeatedly until no spaces remain.
Edit:
Since you have access to C++, Boost has a trim implementation waiting for you to make your life a lot easier.
How about this... It only requires one iteration over the string (doesn't use strlen, which iterates over the string). When the function returns you get a pointer to the start of the trimmed string which is null terminated. The string is trimmed of spaces from the left (until the first character is found). The string is also trimmed of all trailing spaces after the last nonspace character.
char* trim(char* input) {
char* start = input;
while (isSpace(*start)) { //trim left
start++;
}
char* ptr = start;
char* end = start;
while (*ptr++ != '\0') { //trim right
if (!isSpace(*ptr)) { //only move end pointer if char isn't a space
end = ptr;
}
}
*end = '\0'; //terminate the trimmed string with a null
return start;
}
bool isSpace(char c) {
switch (c) {
case ' ':
case '\n':
case '\t':
case '\f':
case '\r':
return true;
break;
default:
return false;
break;
}
}
Not the best way but it works
char* Trim(char* str)
{
int len = strlen(str);
char* buff = new char[len];
int i = 0;
memset(buff,0,len*sizeof(char));
do{
if(isspace(*str)) continue;
buff[i] = *str; ++i;
} while(*(++str) != '\0');
return buff;
}
static inline void ut_trim(char * str) {
char * start = str;
char * end = start + strlen(str);
while (--end >= start) { /* trim right */
if (!isspace(*end))
break;
}
*(++end) = '\0';
while (isspace(*start)) /* trim left */
start++;
if (start != str) /* there is a string */
memmove(str, start, end - start + 1);
}
Here's my implementation, behaving like the built-in string functions in libc (that is, it expects a c-string, it modifies it and returns it to the caller).
It trims leading spaces & shifts the remaining chars to the left, as it parses the string from left to right. It then marks a new end of string and starts parsing it backwards, replacing trailing spaces with '\0's until it finds either a non-space char or the start of the string. I believe those are the minimum possible iterations for this particular task.
// ----------------------------------------------------------------------------
// trim leading & trailing spaces from string s (return modified string s)
// alg:
// - skip leading spaces, via cp1
// - shift remaining *cp1's to the left, via cp2
// - mark a new end of string
// - replace trailing spaces with '\0', via cp2
// - return the trimmed s
//
char *s_trim(char *s)
{
char *cp1; // for parsing the whole s
char *cp2; // for shifting & padding
// skip leading spaces, shift remaining chars
for (cp1=s; isspace(*cp1); cp1++ ) // skip leading spaces, via cp1
;
for (cp2=s; *cp1; cp1++, cp2++) // shift left remaining chars, via cp2
*cp2 = *cp1;
*cp2-- = 0; // mark new end of string for s
// replace trailing spaces with '\0'
while ( cp2 > s && isspace(*cp2) )
*cp2-- = 0; // pad with '\0's
return s;
}
#include "stdafx.h"
#include <string.h>
#include <ctype.h>
char* trim(char* input);
int _tmain(int argc, _TCHAR* argv[])
{
char sz1[]=" MQRFH ";
char sz2[]=" MQRFH";
char sz3[]=" MQR FH";
char sz4[]="MQRFH ";
char sz5[]="MQRFH";
char sz6[]="M";
char sz7[]="M ";
char sz8[]=" M";
char sz9[]="";
char sz10[]=" ";
printf("sz1:[%s] %d\n",trim(sz1), strlen(sz1));
printf("sz2:[%s] %d\n",trim(sz2), strlen(sz2));
printf("sz3:[%s] %d\n",trim(sz3), strlen(sz3));
printf("sz4:[%s] %d\n",trim(sz4), strlen(sz4));
printf("sz5:[%s] %d\n",trim(sz5), strlen(sz5));
printf("sz6:[%s] %d\n",trim(sz6), strlen(sz6));
printf("sz7:[%s] %d\n",trim(sz7), strlen(sz7));
printf("sz8:[%s] %d\n",trim(sz8), strlen(sz8));
printf("sz9:[%s] %d\n",trim(sz9), strlen(sz9));
printf("sz10:[%s] %d\n",trim(sz10), strlen(sz10));
return 0;
}
char *ltrim(char *s)
{
while(isspace(*s)) s++;
return s;
}
char *rtrim(char *s)
{
char* back;
int len = strlen(s);
if(len == 0)
return(s);
back = s + len;
while(isspace(*--back));
*(back+1) = '\0';
return s;
}
char *trim(char *s)
{
return rtrim(ltrim(s));
}
Output:
sz1:[MQRFH] 9
sz2:[MQRFH] 6
sz3:[MQR FH] 8
sz4:[MQRFH] 7
sz5:[MQRFH] 5
sz6:[M] 1
sz7:[M] 2
sz8:[M] 2
sz9:[] 0
sz10:[] 8
I like it when the return value always equals the argument. This way, if the string array has been allocated with malloc(), it can safely be free() again.
/* Remove leading whitespaces */
char *ltrim(char *const s)
{
size_t len;
char *cur;
if(s && *s) {
len = strlen(s);
cur = s;
while(*cur && isspace(*cur))
++cur, --len;
if(s != cur)
memmove(s, cur, len + 1);
}
return s;
}
/* Remove trailing whitespaces */
char *rtrim(char *const s)
{
size_t len;
char *cur;
if(s && *s) {
len = strlen(s);
cur = s + len - 1;
while(cur != s && isspace(*cur))
--cur, --len;
cur[isspace(*cur) ? 0 : 1] = '\0';
}
return s;
}
/* Remove leading and trailing whitespaces */
char *trim(char *const s)
{
rtrim(s); // order matters
ltrim(s);
return s;
}
/* iMode 0:ALL, 1:Left, 2:Right*/
char* Trim(char* szStr,const char ch, int iMode)
{
if (szStr == NULL)
return NULL;
char szTmp[1024*10] = { 0x00 };
strcpy(szTmp, szStr);
int iLen = strlen(szTmp);
char* pStart = szTmp;
char* pEnd = szTmp+iLen;
int i;
for(i = 0;i < iLen;i++){
if (szTmp[i] == ch && pStart == szTmp+i && iMode != 2)
++pStart;
if (szTmp[iLen-i-1] == ch && pEnd == szTmp+iLen-i && iMode != 1)
*(--pEnd) = '\0';
}
strcpy(szStr, pStart);
return szStr;
}
Easiest thing to do is a simple loop. I'm going to assume that you want the trimmed string returned in place.
char *
strTrim(char * s){
int ix, jx;
int len ;
char * buf
len = strlen(s); /* possibly should use strnlen */
buf = (char *) malloc(strlen(s)+1);
for(ix=0, jx=0; ix < len; ix++){
if(!isspace(s[ix]))
buf[jx++] = s[ix];
buf[jx] = '\0';
strncpy(s, buf, jx); /* always looks as far as the null, but who cares? */
free(buf); /* no good leak goes unpunished */
return s; /* modifies s in place *and* returns it for swank */
}
This gets rid of embedded blanks too, if String.Trim doesn't then it needs a bit more logic.
Source: Stackoverflow.com