在C中，可以通过使用格式化字符串函数（如sprintf或snprintf）来实现与Python的f-strings类似的功能。

#include <stdio.h>

int main() {
    char url[200]; // Adjust the size based on your expected URL length
    char keyword[] = "this parameter should be changed each time!";
    char auth[] = "username:password";

    // Construct the URL string with placeholders
    snprintf(url, sizeof(url), "http://website.com/?keyword=%s&auth=%s", keyword, auth);

    // Print the constructed URL
    printf("URL: %s\n", url);

    return 0;
}

字符串