替换字符串中的空格

string replaceNullStr(const char* input){
    size_t srcLen = strlen(input);
    const char* p = input;
    int nullStr = 0;
    while (*p != '\0') {
        if (*p == ' ') {
            ++nullStr;
        }
        ++p;
    }
    size_t outLen = srcLen + 2 * nullStr + 1;
    char outBuff[outLen];

    p = input;
    char* outBuff2 = outBuff;
    while (*p != '\0') {
        if (*p == ' ') {
            strcpy(outBuff2, "%20");
            outBuff2 += 3;
            ++p;
        }else{
            *outBuff2 = *p;
            ++p;
            ++outBuff2;
        }
    }
    return outBuff;
}