为什么值传不过去

我从文件里读入一个数赋值给给定的数GA.adj[i].length和GA.adj[i].speed，最后发现值没有传过去（注：程序前初始化GA.adj[i].speed=0,GA.adj[i].length=1000)GA具体表示的为邻接矩阵表示的图
if((fp=fopen("input.txt","r+"))==NULL)
{
cout<<"Cannot open this file!"<<endl;
exit(0);
}

fscanf(fp,"%d",&totalvex);//读入文件里的第一个数
cout<<"totalvex"<<totalvex<<endl;
initGraph(GA,totalvex);//初始化
fscanf(fp,"%d",&a);
while(a!=-1)//-1为结束符标志
{

//printf("a %d ",a);
fscanf(fp,"%d",&b);
//cout<<"b "<<b<<' ';
cout<<"(a,b)"<<"-->"<<"("<<a<<","<<b<<")"<<endl;
fscanf(fp,"%d",&GA.adj[a*totalvex+b].length);
cout<<"a*totalvex+b="<<a*totalvex+b<<endl;