代码：

void gen_random(char *s, const int len) {
    static const char alphanum[] =
        "0123456789"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz";
    for (int i = 0; i < len; ++i) {
        s[i] = alphanum[rand() % (sizeof(alphanum) - 1)];
    s[len] = 0;
}

这是我用C++11改编的Ates Gral的代码。我在这里添加了lambda，但原则是可以传递它，从而控制字符串包含哪些字符：

std::string random_string( size_t length )
    auto randchar = []() -> char
        const char charset[] =
        "0123456789"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        "abcdefghijklmnopqrstuvwxyz";
        const size_t max_index = (sizeof(charset) - 1);
        return charset[ rand() % max_index ];
    std::string str(length,0);
    std::generate_n( str.begin(), length, randchar );
    return str;
}

下面是将lambda传递给随机字符串函数的示例： http：//ideone.com/Ya8EKf

你为什么要用 C++11 ？

1. 因为可以生成一个 概率分布 (或发行组合)用于感兴趣的字符集。
2. 因为它内置了对 非确定性随机数
3. 因为它支持Unicode，所以可以将其更改为国际化版本。

例如：

#include <iostream>
#include <vector>
#include <random>
#include <functional> //for std::function
#include <algorithm>  //for std::generate_n
typedef std::vector<char> char_array;
char_array charset()
    //Change this to suit
    return char_array( 
    {'0','1','2','3','4',
    '5','6','7','8','9',
    'A','B','C','D','E','F',
    'G','H','I','J','K',
    'L','M','N','O','P',
    'Q','R','S','T','U',
    'V','W','X','Y','Z',
    'a','b','c','d','e','f',
    'g','h','i','j','k',
    'l','m','n','o','p',
    'q','r','s','t','u',
    'v','w','x','y','z'
// given a function that generates a random character,
// return a string of the requested length
std::string random_string( size_t length, std::function<char(void)> rand_char )
    std::string str(length,0);
    std::generate_n( str.begin(), length, rand_char );
    return str;
int main()
    //0) create the character set.
    //   yes, you can use an array here, 
    //   but a function is cleaner and more flexible
    const auto ch_set = charset();
    //1) create a non-deterministic random number generator      
    std::default_random_engine rng(std::random_device{}());
    //2) create a random number "shaper" that will give
    //   us uniformly distributed indices into the character set
    std::uniform_int_distribution<> dist(0, ch_set.size()-1);
    //3) create a function that ties them together, to get:
    //   a non-deterministic uniform distribution from the 
    //   character set of your choice.
    auto randchar = [ ch_set,&dist,&rng ](){return ch_set[ dist(rng) ];};