[C++STDlib基础]关于字符串的操作——C++标准库头文件
网上实例
总结
/* 头文件<cstring> _STD_BEGIN using _CSTD size_t; using _CSTD memchr; using _CSTD memcmp; using _CSTD memcpy; using _CSTD memmove; using _CSTD memset; using _CSTD strcat; using _CSTD strchr; using _CSTD strcmp; using _CSTD strcoll; using _CSTD strcpy; using _CSTD strcspn; using _CSTD strerror; using _CSTD strlen; using _CSTD strncat; using _CSTD strncmp; using _CSTD strncpy; using _CSTD strpbrk; using _CSTD strrchr; using _CSTD strspn; using _CSTD strstr; using _CSTD strtok; using _CSTD strxfrm; _STD_END 共22个函数 拷贝函数(4个)：memcpy,strcpy,strncpy,memmove 连接函数(2个)：strcat,strncat 比较函数(5个)：memcmp,strcmp,strncmp,strxfrm,strcoll 搜索函数(8个)：memchr,strchr,strcspn,strpbrk,strrchr,strspn,strstr,strtok 其他函数(3个)：memset,strerror,strlen */
实例
#include <conio.h>
#include <cstring>
#include <iostream>
using namespace std;
/*拷贝函数
void * memcpy ( void * destination, const void * source, size_t num );//可以复制字符串，结构体等
void * memmove ( void * destination, const void * source, size_t num );
char *strncpy(char *destin, char *source, int maxlen);
*/
void test0()
{
struct
{
char name[40];
int age;
} person, person_copy;
char myname[]="Pierre";
printf("sizeof(myname)=%d,strlen(myname)=%d\n",sizeof(myname),strlen(myname));//7(有结束符) 6
memcpy(person.name,myname,strlen(myname)+1);//strlen(x)只会计算开始到\0之间的字符个数；若不加1，则不会复制结束符，则最后的结果不确定
person.age=54;
memcpy(&person_copy,&person,sizeof(person));
printf("person_copy:%s,%d\n",person_copy.name,person_copy.age);//Pierre 54
char str_copy[15];
char *str1 = "abcdefghi";
strncpy(str_copy, str1, 3);
str_copy[3] = '\0';
printf("%s\n", str_copy); //abc
strcpy(str_copy,str1);
printf("%s\n", str_copy); //abcdefghi
/*复制字符串
1.strcpy的实现
2.while(*p++ = *s++);
直接复制或比较字符串字符会失败
char str1[10], str2[10];
str1 = “abc”;//Error
str2 = str1;//Error
char str3[10] = “abc”;//Ok
#include <string.h> strcpy(超出数组长度后的结果无法预料);strncpy;strcat;strlen;strcmp
*/
}
/*连接函数
char * strcat ( char * destination, const char * source );
char * strncat ( char * destination, const char * source, size_t num );
*/
void test1()
{
char str1[20];
char str2[20];
strcpy (str1,"To be ");
strcpy (str2,"or not to be");
strncat (str1, str2, 6);
puts (str1);//To be or not
}
/*比较函数
int memcmp ( const void * ptr1, const void * ptr2, size_t num );
int strcmp ( const char * str1, const char * str2 );
int strncmp ( const char * str1, const char * str2, size_t num );
*/
void test2()
{
char buffer1[] = "DWgaOtP12df0";
char buffer2[] = "DWGAOTP12DF0";
int m=memcmp ( buffer1, buffer2, sizeof(buffer1) );
if (m>0) printf ("'%s' is greater than '%s'.\n",buffer1,buffer2);//n=1
else if (m<0) printf ("'%s' is less than '%s'.\n",buffer1,buffer2);
else printf ("'%s' is the same as '%s'.\n",buffer1,buffer2);
char str[][5] = { "R2D2" , "C3PO" , "R2A6" };
for (int n=0 ; n<3 ; n++)
{
if (strncmp (str[n],"R2xx",2) == 0)
{
printf ("found %s\n",str[n]);//R2D2 R2A6
}
}
}
/*搜索函数
void * memchr (void * ptr, int value, size_t num );//查找字符
char * strchr (char * str, int character );//查找字符
char * strstr (char * str1, const char * str2 );//查找字符串
*/
void test3()
{
char str[] = "Example string";
char* pch = (char*) memchr (str, 'p', strlen(str));//返回找到的地址
if (pch!=NULL)
printf ("'p' found at position %d.\n", pch-str+1);//5 由于字符串是连续的；所以他们的地址可以相减
else
printf ("'p' not found.\n");
pch=strchr(str,'s');
while (pch!=NULL)
{
printf ("found at %d\n",pch-str+1);//9
pch=strchr(pch+1,'s');
}
pch = strstr (str,"st");
printf("%d\n",pch-str+1);//9
}
/*其他函数
void *memset(void *s, char ch, unsigned n); 设置s中的所有字节为ch, s数组的大小由n给定
char * strerror ( int errnum );
*/
void test4()
{
char str[] = "almost every programmer should know memset!";
memset (str,'-',6);
puts (str);//------ every programmer should know memset!
FILE * pFile;
pFile = fopen ("unexist.ent","r");
if (pFile == NULL)
printf ("Error opening file unexist.ent: %s\n",strerror(errno));//: No such file or directory
/*搜索字符串尾
1.strlen的实现
2.while(*s) s++;
3.while(*s++);
*/
}
void Test(char h)
{
cout<<"press key===="<<h<<endl;
switch(h)
{
case '0': test0();break;
case '1': test1();break;
case '2': test2();break;
case '3': test3();break;
case '4': test4();break;
case 27:
case 'q':exit(0);break;
default:cout<<"default "<<h<<endl;break;
}
}
void main()
{
while(1)
{
Test(getch());
}
}