This is a nice example on how to use the FastCGI library in C.

fcgitest.c

// libfcgi-dev includes
#define NO_FCGI_DEFINES 1
//#include <fcgio.h>
#include <fcgi_config.h>
#include <fcgi_stdio.h>
#include <string.h>

int main()
{
    FCGX_Request request;
    FCGX_Init();
    memset(&request, 0, sizeof(FCGX_Request));

    int sock_fd = FCGX_OpenSocket(":3000", 1024);

    FCGX_InitRequest(&request, sock_fd, 0);

    while(FCGX_Accept_r(&request) == 0)
    {
        const char *qstr = FCGX_GetParam("QUERY_STRING", request.envp);

        FCGX_FPrintF(request.out, "%s", qstr);

        FCGX_Finish_r(&request);
    }

    FCGX_Free(&request, sock_fd);

    return 0;
}