本文实例讲述了C++实现将一个字符串中的字符替换成另一个字符串的方法，分享给大家供大家参考。具体方法如下：

题目要求：

原地实现字符串中的每个空格替换成"%20"，例如输入"We are happy"， 输出"We%20are%20happy"
被替换的字符串当然不仅仅是空格，上面只是个例子
这是道很好的题目，也是百度面试中的一道题，题目不难，但是问题得考虑全面。这里给出如下实现代码：

#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个空格 strcpy(str, " "); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case2: 两个空格 strcpy(str, " "); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case3: 正常情况 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: 没空格 strcpy(str, "wearehappy"); replaceArray(str, src, dest); cout << "str: " << str << endl; replaceArray(str, dest, src); cout << "str: " << str << endl;//case5: 两边一样 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;}

分析上述代码，很有意思的一个情况是srcLen和destLen或大或小的情形，其边界条件的判定不一样。比如we are happy为例子，从后往前拷贝时，count=2。

在count=0时，恰好将最前面的空格替换完成，we则不用重复拷贝。但是对于从前往后拷贝，当count=0时，最后面的happy将不会被拷贝。

希望本文所述实例对大家C++程序算法设计的学习有所帮助。