阅读量:0
把字符串转换为整数
int main() { char pn[21]; cout << "请输入一个由数字组成的字符串： "; cin >> pn; int last = 0; int res[10]; int j = strlen(pn); int idx = 2; cout << "请选择（2-二进制，10-十进制）： "; cin >> idx; for (int i = 0,len = strlen(pn);i < len; i++) { if (pn[i] < '0' || pn[i] > '9') { cout << "非法字符！！！"; break; } last += (pn[i] - '0') * pow(idx,j-1); j = j - 1 ; } cout << last; }重写strcat和strncat
char* mystrcat(char* dest, const char* src) { memcpy(dest + strlen(dest), src, strlen(src) + 1); return dest; } char* mystrncat(char* dest, const char* src, const size_t n) { size_t len = strlen(dest); memcpy(dest + len, src, n); *(dest + len + n) = 0; return dest; }重写strchr和strrchr
注意⚠️：这里不能从后往前找，因为想从后往前找就只能使用strlen，而strlen本质就是遍历一遍字符串，这样就更慢了。
const char* mystrchr(const char* s, int c) { char* p = (char*)s; while (*p) { if (*p == c) return p; p++; } return 0; } const char* mystrrchr(const char* s, int c) //查找字符 { char* p = (char*)s; char* p1 = 0; while (*p) { if (*p == c) { p1 = p; } p++; } return p1; }重写strcmp和strncmp
int mystrcmp(const char* str1, const char* str2) { char* p1 = (char*)str1; char* p2 = (char*)str2; while (*p1 && *p2) { if (*p1 != *p2) { if (*(p1) > *(p2)) return -1; else return 1; } p1++; p2++; } return 0; } int mystrncmp(const char* str1, const char* str2, size_t n) { char* p1 = (char*)str1; char* p2 = (char*)str2; for (int i = 0; i < n; i++) { if (*p1 != *p2) { if (*(p1) > *(p2)) return -1; else return 1; } p1++; p2++; } return 0; }重写strstr
char* caijimystrstr(const char* haystack, const char* needle) { char* p1 = (char*)haystack; char* p2 = (char*)needle; char* tmp1; char* tmp2 = p2; while (*p1) { while (*p1 == *p2) { tmp1 = p1; for (int i = 0; i < strlen(needle); i++) { if (*p1 != *p2) { continue; } p1++; p2++; if (*p2 == 0) { return p1-strlen(needle); } } continue; } p2 = tmp2; p1++; } return nullptr; } const char* dalaomystrstr(const char* haystack, const char* needle) { size_t ii = 0, jj = 0; size_t len = strlen(haystack), slen = strlen(needle); while ((ii < len) && (jj < slen)) { if (haystack[ii] == needle[jj]) { ii++, jj++; } else { ii = ii - jj; jj = 0; ii++; } } if (jj == slen) return (haystack+(ii-jj)); return 0; }解析XML
bool xmlbuffer(const char* xmlbuf, const char* fieldname, char* value = 0, const size_t ilen = 0) { if (xmlbuf == 0 || fieldname == 0) return false; //创建字段 int lenfieldname = strlen(fieldname); //开辟空间 char* sfieldname = new char[lenfieldname + 3]; char* efieldname = new char[lenfieldname + 4]; //初始化 memset(sfieldname, 0, lenfieldname +3); // 错误代码 memset(sfieldname, 0, sfieldname); 原因：new出来的空间不能用memset memset(efieldname, 0, lenfieldname +4); //创建字段 strcpy(sfieldname, "<"); strcat(sfieldname, fieldname); strcat(sfieldname,">"); strcpy(efieldname, "</"); strcat(efieldname, fieldname); strcat(efieldname, ">"); //找字段； char* start; char* end; start = (char*)strstr(xmlbuf, sfieldname); end = (char*)strstr(xmlbuf, efieldname); //没找到 if (start == 0 || end == 0) { delete[] sfieldname; delete[] efieldname; return 0; } size_t vallen = (end - start - lenfieldname - 2); //指针减去指针等于数值，表示的是从 start 到 end 的距离减去了 lenfieldname（<fieldname> 的长度）和 2（< 和 > 的长度）。 if (ilen == 0) { strncpy(value, start + lenfieldname + 2, vallen); value[vallen] = 0; } else if (vallen <= ilen) { strncpy(value, start + lenfieldname + 2, vallen); value[vallen] = 0; } else { strncpy(value, start + lenfieldname + 2, ilen); value[ilen] = 0; } delete[] sfieldname; delete[] efieldname; return 1; }不重复的随机数
void rrand(int arr[], const size_t len, const int minvalue = 0) { srand(time(0)); for (int i = 0; i < len; i++) { while (1) { int tmp = rand() % len + minvalue; int j = 0; for (j = 0; j < i; j++) { if (tmp == arr[j]) break; } if (j == i) { arr[i] = tmp; break; } } } }重写strcpy和strncpy
char* my2strcpy(char* dest, const char* src) { int i = 0; while (src[i]) { dest[i] = src[i]; i++; } dest[i] = 0; return dest; } char* my2strncpy(char* dest, const char* src , const size_t n ) { if (n < 0) return 0; size_t lens = strlen(src); if (n > lens) { my2strcpy(dest, src); } int i = 0; for (i = 0; i < n; i++) { dest[i] = src[i]; } dest[i++] = 0; return dest; }