C++

Forum

 
question about fstream

loveless (56)
i had a question regarding fstream

suppose i had a text file

1 850 9395 11.40am 6
2 900 10000 12.30pm 7
3 900 16800 10.30am 15
.....................

is there any command line that enable us to read a specific row into the program??
Alan (91)
I wrote my own library on this simple problem... use these:

1
2
3
4
5
6
7
8
9
10
11
 
string getLineStr(const char* file, int line) {
  ifstream line_str(file);
  int lineCounter = 0;
    string lineStr;
    while(lineCounter < line) {
         getline(line_str, lineStr);
       ++lineCounter;
    }
    line_str.close();
  return lineStr;     
}


1
2
3
4
5
6
7
8
9
10
11
12
13
 
int getLineInt(const char* file, int line) {
  ifstream line_int(file);
  int lineCounter = 0;
    string lineInt;
    stringstream to_int;
    while(lineCounter < line) {
         getline(line_int, lineInt); 
       ++lineCounter;
    }
    to_int << lineInt;
    line_int.close();
  return atoi(lineInt.c_str());     
}


1
2
3
4
5
6
7
8
9
10
11
 
double getLineDbl(const char* file, int line) {
  ifstream line_dbl(file);
  int lineCounter = 0;
    string lineDbl;
    while(lineCounter < line) {
         getline(line_dbl, lineDbl); 
       ++lineCounter;
    }
    line_dbl.close();
  return atof(lineDbl.c_str());  
}


they are simple implementations but they get the job done. :)

PS... to set a specific line use these:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
 
void setLine(const char* file, string val, int line) {
  ifstream line_file(file);
     string fileStr;
     string lineStr;
     int counter = 1;
          while(!line_file.eof()) {
               if(counter != line) {
                         getline(line_file, lineStr);
                      lineStr += "\n";
                      
                    if(counter == line+1) {
                         lineStr.clear();
                    }
               } else {
                    lineStr = val + "\n";
               }        
            fileStr += lineStr;
            lineStr.clear();
            ++counter;
          }
     fileClear(file);
     lineStr.erase(lineStr.length());
     setStr(file, fileStr);
     line_file.close();
}


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
 
void setLine(const char* file, int val, int line) {
  ifstream line_file(file);
     string fileStr;
     string lineStr;
     int counter = 1;
          while(!line_file.eof()) {
               if(counter != line) {
                         getline(line_file, lineStr);
                      lineStr += "\n";
                      
                    if(counter == line+1) {
                         lineStr.clear();
                    }
               } else {
                    lineStr = itoa(val) + "\n";
               }        
            fileStr += lineStr;
            lineStr.clear();
            ++counter;
          }
     fileClear(file);
     lineStr.erase(lineStr.length());
     setStr(file, fileStr);
     line_file.close();
}


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
 
void setLine(const char* file, double val, int line) {
  ifstream line_file(file);
     string fileStr;
     string lineStr;
     int counter = 1;
          while(!line_file.eof()) {
               if(counter != line) {
                         getline(line_file, lineStr);
                      lineStr += "\n";
                      
                    if(counter == line+1) {
                         lineStr.clear();
                    }
               } else {
                    lineStr = dtostr(val) + "\n";
               }        
            fileStr += lineStr;
            lineStr.clear();
            ++counter;
          }
     fileClear(file);
     lineStr.erase(lineStr.length());
     setStr(file, fileStr);
     line_file.close();
}


WARNING@@@!!!!! If more than one source is setting a file using setLine() there is a danger of the file being corupted!!!! (Never got around to making a completely safe one...)
Last edited on
loveless (56)
....can i know what is the use of 'val' in the last three source code??
Alan (91)
in the last 3 val is what row line is set to

setLine("text.txt", "12:00", 2);

sets row 2 to "12:00".
Last edited on
loveless (56)
oo~~~~ i see~~~~~~~
thanks Alan~~~~~
i'll give it a try at this~~~~~~~
loveless (56)
thanks again Alan~~~~~

now i know how to continue my assignment again :D
Alan (91)
no prob
Topic archived. No new replies allowed.