本文實例講述了C++實現將一個字符串中的字符替換成另一個字符串的方法，分享給大家供大家參考。具體方法如下：
題目要求：
原地實現字符串中的每個空格替換成"%20"，例如輸入"We are happy"， 輸出"We%20are%20happy"
被替換的字符串當然不僅僅是空格，上面只是個例子
這是道很好的題目，也是百度面試中的一道題，題目不難，但是問題得考慮全面。這里給出如下實現代碼：
#include <iostream>#include <vector>#include <cassert>using namespace std;int findNumberFirst(const char *str, const char *dest, vector<int>& pvec){ if (str == NULL || dest == NULL) return 0; int pos = 0; int lenStr = strlen(str); int lenDest = strlen(dest); if (lenStr < lenDest) return 0; int count = 0; while (pos <= lenStr - lenDest) { if (strncmp(str + pos, dest, strlen(dest)) == 0) { pvec.push_back(pos); pos += lenDest; count++; } else { pos++; } } return count;}int findNumberLast(const char *str, const char *dest, vector<int> &pvec){ if (str == NULL || dest == NULL) return 0; int strLen = strlen(str); int destLen = strlen(dest); if (strLen < destLen) return 0; int pos = 0; while (pos <= strLen - destLen) { if (strncmp(str + pos, dest, strlen(dest)) == 0) { pos += destLen; pvec.push_back(pos - 1); } else { pos++; } } return pvec.size();}void replaceArray(char *str, const char *src, const char *dest){ if (str == NULL || src == NULL || dest == NULL) return; vector<int> pvec; int strLen = strlen(str); int srcLen = strlen(src); int destLen = strlen(dest); if (strLen < srcLen) return; int posBefore = 0; int posAfter = 0; if (srcLen < destLen) { int count = findNumberLast(str, src, pvec); if (count <= 0) return; posAfter = strLen + count * (destLen - srcLen) - 1; posBefore = strLen - 1; while (count > 0 && posBefore >= 0) { if (pvec[count - 1] == posBefore) { posAfter -= destLen; strncpy(str + posAfter + 1, dest, strlen(dest)); count--; posBefore--; } else { str[posAfter--] = str[posBefore--]; } } } else if (strLen > destLen) { int count = findNumberFirst(str, src, pvec); if (count <= 0) return; posAfter = 0; posBefore = 0; int i = 0; while (count >= 0 && posBefore < strLen) { if (count > 0 && pvec[i] == posBefore) { strncpy(str + posAfter, dest, strlen(dest)); posAfter += destLen; count--; posBefore += srcLen; i++; } else { str[posAfter++] = str[posBefore++]; } } str[posAfter] = '/0'; }}void main(){ char *str = new char[100]; if (str == NULL) return; memset(str, '/0', 100); const char *src = " "; const char *dest = "%20";//case1: 只有1個空格 strcpy(str, " "); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case2: 兩個空格 strcpy(str, " "); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case3: 正常情況 strcpy(str, "we are happy"); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case3: 空格在前 strcpy(str, " we are happy"); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case4: 空格在后 strcpy(str, "we are happy "); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case4: 沒空格 strcpy(str, "wearehappy"); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case5: 兩邊一樣 strcpy(str, "we are happy"); replaceArray(str, src, dest); cout << "str: " << str << endl; src = "%20"; assert(dest == "%20"); replaceArray(str, dest, src); cout << "str: " << str << endl;}分析上述代碼，很有意思的一個情況是srcLen和destLen或大或小的情形，其邊界條件的判定不一樣。比如we are happy為例子，從后往前拷貝時，count=2。
在count=0時，恰好將最前面的空格替換完成，we則不用重復拷貝。但是對于從前往后拷貝，當count=0時，最后面的happy將不會被拷貝。
希望本文所述實例對大家C++程序算法設計的學習有所幫助。
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