随机字符串。

static char char_flag;// 1111 ,figure ,lowercase ,uppercase,special char
std::string generateString(){
    std::string result = "";
    srand((unsigned)time(NULL));
    char_flag = 0;

    for(int i=0; i<8; i++){
    char c =  rand()%(127-33)+33;

    if(c >=48 &&c <= 57){
            char_flag = char_flag|8;
    }else if(c >= 65 && c <= 90){
            char_flag = char_flag|2;
    }else if(c >= 97 && c <= 122){
            char_flag = char_flag|4;
    }else{
            char_flag = char_flag|1;
        }
        result += c;
    }
    if(char_flag == 0xf)
        return result;
    if(char_flag %2 == 0){
        char c =  rand()%(127-33)+33;
    while((c>=48&& c<= 57 )|| (c>=65&&c<=90)||(c>=97&&c<=122)){
            c =  rand()%(127-33)+33;
    }
        result +=  c;    
    }
    if((char_flag>>1 )%2 == 0){
        char c =  rand()%(91-65)+65;
        result += c;            
    }
    if((char_flag>>2) %2 == 0){
        char c =  rand()%(127-97)+97;
        result +=  c;                
    }
    if((char_flag>>3 )%2 == 0){
        char c =  rand()%(58-48)+48;
        result += c;                
    }
    result+="\0";
    SVP_INFO("------size = %d ----rand() = %s",result.size(),result.c_str());
    return result;
}