Pegando dados enviados usando o método POST

#include <stdio.h>
#include <stdlib.h>

int main() {
    char *string = getenv( "CONTENT_LENGTH" );
    int tamanho  = atoi( string );

    char vetor[tamanho + 1];

    fgets( vetor, tamanho + 1, stdin );

    printf( "Content-type: text/html\n\n" );
    printf( "<html>\n" );
    printf( "\t<head>\n" );
    printf( "\t\t<meta charset=\"UTF-8\">\n" );
    printf( "\t\t<title>Lendo dados do formulário</title>\n" );
    printf( "\t</head>\n" );
    printf( "\t<body>\n" );
    printf( "\t\t<h1>Olá mundo!</h1>\n" );
    printf( "\t\t<h1>Estou lendo: %s</h1>\n", vetor );
    printf( "\t</body>\n" );
    printf( "</html>\n" );
    printf( "\n\n" );

    return 0;
}