openssl验证证书，c语言代码怎么实现

对于您的问题，我可以提供以下代码实现：

#include <openssl/x509.h>
#include <openssl/pem.h>

int verify_callback(int preverify_ok, X509_STORE_CTX *ctx) {
    if (preverify_ok == 0) {
        int err = X509_STORE_CTX_get_error(ctx);
        printf("Verification failed: %d\n", err);
    }
    return preverify_ok;
}

int verify_certificate(const char *cert_file_path, const char *ca_cert_file_path) {
    int ret = 1;

    // Load the certificate from the file
    FILE *cert_file = fopen(cert_file_path, "r");
    if (cert_file == NULL) {
        printf("Failed to open certificate file %s\n", cert_file_path);
        return 0;
    }
    X509 *cert = PEM_read_X509(cert_file, NULL, NULL, NULL);
    fclose(cert_file);

    // Load the CA certificate from the file
    FILE *ca_cert_file = fopen(ca_cert_file_path, "r");
    if (ca_cert_file == NULL) {
        printf("Failed to open CA certificate file %s\n", ca_cert_file_path);
        X509_free(cert);
        return 0;
    }
    X509 *ca_cert = PEM_read_X509(ca_cert_file, NULL, NULL, NULL);
    fclose(ca_cert_file);

    // Create a certificate store and add the CA certificate
    X509_STORE *store = X509_STORE_new();
    X509_STORE_add_cert(store, ca_cert);

    // Create a verification context and set the callback function
    X509_STORE_CTX *ctx = X509_STORE_CTX_new();
    X509_STORE_CTX_init(ctx, store, cert, NULL);

    X509_STORE_CTX_set_verify_cb(ctx, verify_callback);

    // Perform the verification
    if (X509_verify_cert(ctx) != 1) {
        printf("Certificate verification failed!\n");
        ret = 0;
    } else {
        printf("Certificate verification succeeded!\n");
    }

    // Clean up
    X509_STORE_CTX_free(ctx);
    X509_STORE_free(store);
    X509_free(cert);
    X509_free(ca_cert);

    return ret;
}

该代码使用 OpenSSL 库实现了对证书的验证，它假定您已经安装了 OpenSSL 库，因此需要包含 `<openssl/x509.h>` 和 `<openssl/pem.h>`。该代码使用 `verify_certificate` 函数，您需要传递要验证的证书文件路径和 CA 证书文件路径。如果验证失败，函数会返回 0，否则会返回 1。注意，该函数在执行之前需要确保证书文件和 CA 证书文件存在且可读。