strlen(char* a); --------------------- String length
strcpy(char* a,char* b); ----- ---------string assignment (original or current input)
strncpy(char* a,char* b,int c);-------string assignment, take the first c ( Original or current input)
strcat(char* a, char* b); ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ The string is copied after the existing string (the original or current input )
strncat(char* a,char* b,int c);---------Copy the string behind the existing string, take the first c ones (original or current input)
strcmp(char* a, char* b); -------------- Compare the size of characters and output the result, greater than output 1, equal to output 0, less than output -1
strchr(char* a,int c) ;--------------------Find the first character to the end (use ASCII to represent the first character)
strrchr(char* a,int c);- ------------------Find the last character from the beginning to the end (use ASCII to represent the last character)
strstr;(char* a,char* b); ---- -----------Find the string and output to the end.
#include <stdio.h> //自定义string子函数模块
#include <stdlib.h>
#include <math.h>
#include <string.h>
//strlen
char len(char* a)
{
int i;
for(i=0;;i++)
if(a[i]==0) break; //==0 or =='\0'
return i;
}
//strcpy
char* cpy(char* a,char* b)
{
int i;
//while(str[i]!=0) {dest[i]=str[i];i++;}
//dest[i]=0;
for(i=0;;i++)
{
if(b[i]!=0) a[i]=b[i];
else break; //for循环必须要有终止条件！
}
a[i]=0;
return a;
}
//strncpy
char* ncpy(char* a,char* b,int c)
{
int i;
//while(str[i]!=0) {dest[i]=str[i];i++;}
//dest[i]=0;
for(i=0;;i++)
{
if(i!=c) a[i]=b[i];
else break; //for循环必须要有终止条件！
}
a[i]=0;
return a;
}
//strcat
char* cat(char* a,char* b)
{
int i=0,k=len(a);
for(i=0;;i++)
{
if(b[i]!='\0') a[k+i]=b[i];
else break;
}
return a;
}
//strncat
char* ncat(char* a,char* b, int c)
{
int i=0,k=len(a);
for(i=0;;i++)
{
if(b[i]!='\0') a[k+i]=b[i];
if(i==c-1) break;
}
return a;
}
//strcmp
char* cmp(char* a,char* b)
{
int i,k=len(a)>=len(b)?len(a):len(b);
//printf("k=%d ",k);
for(i=0;i<k;i++)
{
//printf("a[i]=%d b[i]=%d\n",a[i],b[i]);
if(a[i]==b[i]) continue;
else if(a[i]>b[i]) return 1;
else if(a[i]<b[i]) return -1;
}
if(a[i]==b[i]) return 0;
return a;
}
//strchr_1
char* chr_1(char* a,int b) //不需要printf，直接输出
{
int i,j=-1,k=len(a);
for(i=0;i<k;i++)
{
if(a[i]==b)
{
//printf("第%d个开始替换\n",i);
for(j=0;j<k-i;j++)
printf("%c",a[i+j]); //a[i]表示的是一个字符而不是字符串所以是%c而不是%s 切记！
}
if(j==k-i) break;
}
return a;
}
//strchr_2
char* chr_2(char* a,int b) //不需要printf，直接输出
{
int i,j=-1,k=len(a);
for(i=0;i<k;i++)
{
if(a[i]==b)
{
//printf("\n第%d个开始替换\n",i);
for(j=0;j<k-i;j++)
a[j]=a[j+i];
int t;
for(t=k-1;t>=k-i;t--)
a[t]='\0';
}
if(j==k-i) break;
}
return a;
}
//strrchr
//strrchr和strchr的不同之处在于前者没有（本行+16）行的if break终止
//它会直接到最后一个输入的ASCII值并开始输出到末尾。
//而且strrchr也同样可以通过字符%c直接输出，不需要for循环,具体见上二个子函数。
char* rchr_1(char* a,int b) //法1
{
int i,j,k=len(a);
for(i=0;i<k;i++)
{
if(a[i]==b) //如果变成if(a[i]==b) a[i]=='\0' else的话，那么在最后到达所需字符的ASCII码后，
{
//仍会将后面的不等于相应ASCII码的初始化，因为没有if break终止。
//printf("\n第%d个开始替换\n",i);
for(j=0;j<k-i;j++)
a[j]=a[j+i];
int t;
for(t=k-1;t>=k-i;t--)
a[t]='\0';
}
//if(j==k-i) break;
}
return a;
}
char* rchr_2(char* a,int b) //法2,逆向求法
{
int i,j,t,k=len(a);
for(i=1;i<k;i++) if(a[k-i]==b) {
t=k-i; break;} //printf("k=%d %d %d\n",k,t,k-i);
if(i==k)return 0;
for(j=0;j<i;j++) a[j]=a[j+t];//{printf("%c",a[j+t]);}
for(i=1;i<=t;i++) a[k-i]='\0';
return a;
}
char* str(char* a,char* b)
{
int i,j,t,s,ka=len(a),kb=len(b);
for(i=0;i<ka;i++)
{
for(j=0;j<kb && a[i+j]==b[j];j++){
s=i;t=j;}if(j==kb) break;}//if(j==kb) break;}
//if(t==kb-1)
if(j==kb)
//for(i=0;i<ka-kb;i++) {printf("%c",a[s+i]);break;} //单个字母直接输出。
{
for(i=0;i<ka;i++) {
a[i]=a[i+s];}}
else return 0;
return a;
}
int main() //测试上述自定义的字符串函数
{
char a[100],b[100],c[100];
int m;
memset(a,0,sizeof(a));memset(b,0,sizeof(b));memset(c,0,sizeof(c));
printf("%d %d\n",len(""),len("北京欢迎你！"));
cpy(a,"hello");
ncpy(b,"world!",4);
printf(" cpy a is %s\n",a);
printf("ncpy b is %s\n",b);
cpy(c,"hello ");
cat(c,"world!");
printf(" cat c is %s\n",c);
ncat(c,a,4);
printf("ncat c is %s\n",c);
memset(a,0,sizeof(a));memset(b,0,sizeof(b));memset(c,0,sizeof(c));
cpy(a,"Abcd");cpy(b,"Abc");cpy(c,"Bac");
printf("%d\n",cmp(a,b));
printf("%d\n",cmp(b,c));
printf("%d\n",cmp(c,c));
cpy(b,"What is your name? 3.1415926535897932384626433832795028841971693993751");
cpy(a,b); printf("\n方法1："); chr_1(a,97);
cpy(a,b); printf("\n方法2：%s", chr_2(a,97));
cpy(a,b); printf("\n方法1：%s",rchr_1(a,97));
cpy(a,b); printf("\n方法2：%s\n",rchr_2(a,97));//rchr_2(a,97); //将97换成'p'时，由于字符串中没有'p'，输出Null，以上同理但未设置。
cpy(a,b); printf("\n查找2=%s",str(a,"name"));
//printf("\n查找1="); str(a,"name");
cpy(a,b); printf("\n%s",ncpy(c,a+5,18));
memset(c,0,sizeof(c));cpy(c,"Bac");
cpy(a,b); printf("\n%s",ncat(c,a+5,13)); //自定义的cvpy以及ncat可以直接移动截断？
}
Wrote it a long time ago, and posting it now.
If you have any opinions and suggestions, please point out and comment, because I may not remember clearly.