C language implementation: extract public key and private key factors from sm2 PEM file

We know that using the openssl command line to extract the public key and private key factor from the pem of the national secret sm2 is as follows:

• openssl ec -in sm2_test_priv.pem -text -nooutExtract private key from private key pem
• openssl ec -pubin -in sm2_test_pub.pem -text -nooutExtract public key from public key pem

Taking private key extraction as an example, how to implement the above part in C language? The following is a reference example written for everyone:

#include <stdio.h>
#include <stdlib.h>
#include <openssl/rsa.h>
#include <openssl/pem.h>

int main() {
    
    
    const char *filename = "test_priv.pem"; // 替换为你的PEM文件路径

    // 打开PEM文件
    FILE *file = fopen(filename, "r");
    if (!file) {
    
    
        perror("Error opening file");
        return 1;
    }

    // 从PEM文件中读取RSA私钥
    RSA *rsa_private_key = PEM_read_RSAPrivateKey(file, NULL, NULL, NULL);
    fclose(file);

    if (!rsa_private_key) {
    
    
        ERR_print_errors_fp(stderr);
        return 1;
    }

    // 输出私钥信息
    printf("RSA Private Key:\n");
    RSA_print_fp(stdout, rsa_private_key, 0);

    // 释放私钥内存
    RSA_free(rsa_private_key);

    return 0;
}

Compile command:gcc main.c -o x -lssl -lcrypto