字符串连接与转换实践-优快云博客

char* strcat(char* s1,char *s2) { char* ptr; ptr = s1; while(*ptr != '/0') ptr ++; while(*s2 != '/0') *ptr ++ = *s2 ++; *ptr = '/0'; return s1; } void main() { char d[20],s[20]; char *ret; strcpy(d,"this is"); strcpy(s," a string"); ret = strcat(d,s); printf("%s/n",ret); getchar(); }

上面是我进过n次修改后的程序，在写这个程序中我遇到了下面几个问题

ptr到底指向哪里，虽然有(*s1 != '/0') s1++ ，那么s1最后指向的是'/0'

又 while(*s2 != '/0') *ptr ++ = *s2 ++;那么ptr又是指向的哪里，很明显ptr不指向的是'/0' 因此最后应该*ptr = '/0'，而不是*(ptr + 1) = '/0';

错误二 ptr在循环 *ptr != '/0'的时候 *ptr的值为's' ，因此 *ptr ++ = *s2++ 之后 *ptr的值为多少喃？再加上一个'/0',来我告诉你答案是“”;那么s1为多少？注意 s2将其内容复制到s1后面的空间了，那么s1后面的空间又是什么喃，有高手是这样回答的：

高地址

环境变量
命令行参数
指向环境变量的指针
指向命令行参数的指针
程序名称(即main)
main参数等

低地址

下面有一组测试数据:

char d[1024] = "this is aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
char s[2048] =" a string ggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggx";
那么上面的程序就会报错

所以我采用了另外一种方法：

char* myStrcat( const char* s1,const char * s2,int n) { char dest[3072]; char *ptr ; ptr = dest; while(*s1 != '/0') { *ptr++ = *s1++; } while(*s2 != '/0') { *ptr ++ = *s2++; } *ptr = '/0'; return dest; }

该方法就ok 不过可能要数组会溢出,这里还有个注意的地方

刚开始我采用的是这样的方法：

int n = strlen(s1) + strlen(s2);

char dest[n+1];该方法在编译时就不能通过

将大小写互换：

char* convert(char * source) { char* ptr; ptr = source; char c_char; while(*ptr != '/0') { c_char = *ptr; if((c_char >='A' && c_char<='Z' )|| (c_char >= 'a'&& c_char <='z' )) { if(c_char >= 'a'&& c_char <='z') *ptr = c_char -32; else *ptr = c_char +32; } ptr ++; } *ptr = '/0'; return source; }

写这个程序的主要目的是将一个字面值赋值一个char*指针，那么该指针将能不被作为const类型;如果要修改字面值，必须将字符指针转换为char数组