C语言中删去字符串头部空格的方法
C语言没有提供可删去字符串头部空格的标准库函数，但是，编写这样的一个函数是很方便的。请看下例；
#include <stdio. h>
#include <string. h>
void main(void);
char * ltrim (char * ) ;
char * rtrim(char * ) ;
void main (void)
{
char * lead_str = " This string has leading spaces in it. " ;,
/ * Show the status of the string before calling the Itrim()
function. * /
printf("Before calling Itrim(), lead-str is '%s'\n", lead_str);
printf("and has a length of %d. \n" , strlen(lead_str));
/ * Call the Itrim() function to remove the leading blanks. * /.
Itrim(lead_str);
/ * Show the status of the string
after calling the Itrim() function. * /
prinft("After calling Itrim(), lead_str is '%s'\n", lead_str);
print("and has a length of %d. \n'' , strlen(lead-str)) ;
}
/ * The Itrim() function removes leading spaces from a string. * /
char * ltrim(char * str)
{
strrev(str) ; / * Call strrevO to reverse the string. * /
rtrim(str)). /* Call rtrimO to remvoe the "trailing" spaces. * /
strrev(str); / * Restore the string's original order. * /
return str ; / * Return a pointer to the string. * /.
}
/ * The rtrim() function removes trailing spaces from a string. * /
char* rtrim(char* str)
{
int n = strlen (str)-l ; / * Start at the character BEFORE
the null character (\0). * /
while (n>0) / * Make sure we don't go out of bounds... * /.
{
if ( * (str+n) ! =' ') If we find a nonspace character: * /
{
* (str+n + 1) = '\0' ; / * Put the null character at one
character past our current
position. * /
break;j / * Break out of the loop. * /
}
else / * Otherwise, keep moving backward in the string. * /
n --;
}
return str； /* Return a pointer tO the string． */
}
在上例中，删去字符串头部空格的工作是由用户编写的ltrim()函数完成的，该函数调用了·6．2的例子中的rtrim()函数和标准C库函数strrev()。ltrim()函数首先调用strrev()函数将字符串颠倒一次，然后调用rtrim()函数删去字符串尾部的空格，最后调用strrev()函数将字符串再颠倒一次，其结果实际上就是删去原字符串头部的空格。
#include <stdio. h>
#include <string. h>
void main(void);
char * ltrim (char * ) ;
char * rtrim(char * ) ;
void main (void)
{
char * lead_str = " This string has leading spaces in it. " ;,
/ * Show the status of the string before calling the Itrim()
function. * /
printf("Before calling Itrim(), lead-str is '%s'\n", lead_str);
printf("and has a length of %d. \n" , strlen(lead_str));
/ * Call the Itrim() function to remove the leading blanks. * /.
Itrim(lead_str);
/ * Show the status of the string
after calling the Itrim() function. * /
prinft("After calling Itrim(), lead_str is '%s'\n", lead_str);
print("and has a length of %d. \n'' , strlen(lead-str)) ;
}
/ * The Itrim() function removes leading spaces from a string. * /
char * ltrim(char * str)
{
strrev(str) ; / * Call strrevO to reverse the string. * /
rtrim(str)). /* Call rtrimO to remvoe the "trailing" spaces. * /
strrev(str); / * Restore the string's original order. * /
return str ; / * Return a pointer to the string. * /.
}
/ * The rtrim() function removes trailing spaces from a string. * /
char* rtrim(char* str)
{
int n = strlen (str)-l ; / * Start at the character BEFORE
the null character (\0). * /
while (n>0) / * Make sure we don't go out of bounds... * /.
{
if ( * (str+n) ! =' ') If we find a nonspace character: * /
{
* (str+n + 1) = '\0' ; / * Put the null character at one
character past our current
position. * /
break;j / * Break out of the loop. * /
}
else / * Otherwise, keep moving backward in the string. * /
n --;
}
return str； /* Return a pointer tO the string． */
}
在上例中，删去字符串头部空格的工作是由用户编写的ltrim()函数完成的，该函数调用了·6．2的例子中的rtrim()函数和标准C库函数strrev()。ltrim()函数首先调用strrev()函数将字符串颠倒一次，然后调用rtrim()函数删去字符串尾部的空格，最后调用strrev()函数将字符串再颠倒一次，其结果实际上就是删去原字符串头部的空格。
