???? (关于一段C程序）

lzhxin

// example of macro to read data from an ascii file and
// create a root file with a Tree.
// see also a variant in cernbuild.C
// Author: Rene Brun
void staff() {

struct staff_t {
Int_t Category;
UInt_t Flag;
Int_t Age;
Int_t Service;
Int_t Children;
Int_t Grade;
Int_t Step;
Int_t Hrweek;
Int_t Cost;
Char_t Division[4];
Char_t Nation[3];
};

staff_t staff;

//The input file cern.dat is a copy of the CERN staff data base
//from 1988
FILE *fp = fopen("cernstaff.dat","r");

char line[80];

TFile *f = new TFile("staff.root","RECREATE");
TTree *tree = new TTree("T","staff data from ascii file");
tree->Branch("staff",&staff.Category,"Category/I:Flag:Age:Service:Children:Grade:Step:Hrweek:Cost");
tree->Branch("Division",staff.Division,"Division/C");
tree->Branch("Nation",staff.Nation,"Nation/C");
//note that the branches Division and Nation cannot be on the first branch
while (fgets(&line,80,fp)) {
sscanf(&line[0],"%d %d %d %d %d",&staff.Category,&staff.Flag,&staff.Age,&staff.Service,&staff.Children);
sscanf(&line[32],"%d %d %d %d %s %s",&staff.Grade,&staff.Step,&staff.Hrweek,&staff.Cost,staff.Division,staff.Nation);
tree->Fill();
}
tree->rint();
tree->Write();

fclose(fp);
delete tree;
delete f;
}

在程序中 char line[80];定义了一个字符数组，长度为80
程序
while (fgets(&line,80,fp)) {
sscanf(&line[0],"%d %d %d %d %d",&staff.Category,&staff.Flag,&staff.Age,&staff.Service,&staff.Children);
sscanf(&line[32],"%d %d %d %d %s %s",&staff.Grade,&staff.Step,&staff.Hrweek,&staff.Cost,staff.Division,staff.Nation);
tree->Fill();
}
中
1。while (fgets(&line,80,fp))意思是什么？
2。 sscanf(&line[0],"%d %d %d %d %d",&staff.Category,&staff.Flag,&staff.Age,&staff.Service,&staff.Children);
中的&line[0]更是不明白了？请问是什么意思？
3。sscanf(&line[32],"%d %d %d %d %s %s",&staff.Grade,&staff.Step,&staff.Hrweek,&staff.Cost,staff.Division,staff.Nation);
中的&line[32]同样不明白，请问是什么意思？
谢谢phenixwutao！

manphiz

$ man fgets
$ man sscanf
如果可能，请阅K&R C

MatthewGong

&line[0] == line

&line[32] == line+32

这种写法是取数组中某一个元素的地址的写法（[]接合度比&高， sscanf后面要的是对应类型的指针）。
很少有人采用这种书写方法（我只在4年前老师上C++的课上听到过这种写法）。

rickxbx

Post by lzhxin

1。while (fgets(&line,80,fp))意思是什么？
2。 sscanf(&line[0],"%d %d %d %d %d",&staff.Category,&staff.Flag,&staff.Age,&staff.Service,&staff.Children);
中的&line[0]更是不明白了？请问是什么意思？
3。sscanf(&line[32],"%d %d %d %d %s %s",&staff.Grade,&staff.Step,&staff.Hrweek,&staff.Cost,staff.Division,staff.Nation);
中的&line[32]同样不明白，请问是什么意思？
谢谢phenixwutao！

line[0],line[32] 都是char,前面加一个&,自然就变成了char*