string str="123abc456"; int i=3;1 取字符串的前i个字符
str=str.Substring(0,i); // or str=str.Remove(i,str.Length-i);
2 去掉字符串的前i个字符：
str=str.Remove(0,i); // or str=str.Substring(i);
3 从右边开始取i个字符：
str=str.Substring(str.Length-i); // or str=str.Remove(0,str.Length-i);
4 从右边开始去掉i个字符：
str=str.Substring(0,str.Length-i); // or str=str.Remove(str.Length-i,i);
5 判断字符串中是否有"abc" 有则去掉之
using System.Text.RegularExpressions;
string str = "123abc456";
string a="abc";
Regex r = new Regex(a);
Match m = r.Match(str);
if (m.Success) {//二选一
str=str.Replace(a,"");
Response.Write(str);
//或者：string str1,str2;
str1=str.Substring(0,m.Index);
str2=str.Substring(m.Index+a.Length,str.Length-a.Length-m.Index);
Response.Write(str1+str2);
}
6 如果字符串中有"abc"则替换成"ABC"
str=str.Replace("abc","ABC");
7. 根据分隔符截取字符串，strtok()函数。
#include <iostream>
#include <cstring>
using namespace std;
int main()
{
char sentence[]="This is a sentence with 7 tokens";
cout<<"The string to be tokenized is:\n"<<sentence<<"\n\nThe tokens are:\n\n";
char *tokenPtr=strtok(sentence," ");
while(tokenPtr!=NULL)
{
cout<<tokenPtr<<\'\n\';
tokenPtr=strtok(NULL," ");//固定写法，可直接记住
}
cout<<"After strtok, sentence = "<<sentence<<endl;
return 0;
}