Five methods of random number generation in C/C++

C/C++ Random number generation method

1. Use rand() and srand()

Library: <>or<cstdlib>
Features: Pseudo-random number generator, simple and easy to use.
Example:

#include &lt;&gt;
#include &lt;&gt;

int main() {
    srand(time(NULL));  // Initialize the random number generator    int random_number = rand() % 100;  // Generate random numbers between 0 and 99    printf("Random number: %d\n", random_number);
    return 0;
}

2. Use the <random> library

Library: <random>
Features: Provides a variety of random number generators and distributions.
Example:

#include &lt;random&gt;
#include &lt;iostream&gt;

int main() {
    std::random_device rd;  // True random number generator    std::mt19937 gen(rd()); // Mersenne Twister Engine    std::uniform_int_distribution&lt;&gt; dis(0, 99);  // Generate integers between 0 and 99
    int random_number = dis(gen);
    std::cout &lt;&lt; "Random number: " &lt;&lt; random_number &lt;&lt; std::endl;
    return 0;
}

3. Use /dev/random and /dev/urandom

Library: No special libraries are needed, they are read directly through file operations.
Features: Provides true random numbers.
Example:

#include <>
#include <>

int main() {
    FILE *file = fopen("/dev/urandom", "rb");
    unsigned char random_byte;
    if (fread(&random_byte, 1, 1, file) != 1) {
        perror("fread");
        exit(EXIT_FAILURE);
    }
    fclose(file);

    int random_number = random_byte % 100;
    printf("Random number: %d\n", random_number);
    return 0;
}

4. Generate instructions using hardware random numbers

Library: <>
Features: Provides true random numbers at the hardware level.
Example:

#include &lt;&gt;
#include &lt;&gt;

int main() {
    unsigned int random_number;
    _rdrand32_step(&amp;random_number);  // It may take multiple attempts to succeed    printf("Random number: %u\n", random_number % 100);
    return 0;
}

5. Use the OpenSSL library

Library: <openssl/>
Features: Provides high-quality random numbers for encryption.
Example:

#include &lt;openssl/&gt;
#include &lt;&gt;

int main() {
    unsigned char random_bytes[4];  // Generate 4 byte random number    if (!RAND_bytes(random_bytes, sizeof(random_bytes))) {
        printf("RAND_bytes failed\n");
        return 1;
    }

    unsigned int random_number = *(unsigned int *)random_bytes;
    printf("Random number: %u\n", random_number % 100);
    return 0;
}

Select the appropriate random number generation method

Pseudo-random number generator (rand(), <random>): Suitable for occasions where there is little requirement for randomness, such as simple random events in game development.
True random number generator (/dev/urandom, OpenSSL, Hardware Random Number Generator): Suitable for occasions with high security requirements, such as cryptography applications and encryption key generation.

Things to note

use/dev/randomWhen paying attention, if the entropy in the system entropy pool is not enough, read/dev/randomMay be blocked until there is enough entropy generated.
For safety-sensitive applications, use should be avoided.rand()andsrand(), because they generate pseudo-random numbers and are not suitable for encryption.
When selecting a random number generator, the balance between performance and security is taken into account.

These methods cover different scenarios from simple pseudo-random numbers to high-quality true random numbers generation.

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