File Reading

[euacela1]

Can someone tell me please hoe can I read from a file from a certain line. How can I make the cursor that reads to a certain line?
The only fumtion I know is fscanf() and the only one that seeks if fseek() but fseek is a function that jump over kb-s And I need something to take me to a certain line.
Tahnk you.

 

[Salem]

A for loop and fgets() is the only easy way to get to a specific line within a file.

If you're doing this a lot (and the text file is fairly static), then you can build an index, which will allow you to fseek() to a line of your choice.

--

 

[teriviret]

If you don't mind using the Win32 API (CreateFile, ReadFile, etc.) for files rather than the runtime library (fopen, fread, etc.), here is another way to search for a specific line in a file. First, map the file into memory using MapViewOfFile. Then, in a loop, scan the mapped memory, counting the number of newline characters (ASCII code 0x0A). When the count reaches the desired line number minus one, stop scanning the file.

Here is an example (not tested and does not handle exceptional conditions):

HANDLE in = CreateFile ("myfile.txt", GENERIC_READ, FILE_SHARE_READ,
                        NULL, OPEN_EXISTING,
                        FILE_ATTRIBUTE_NORMAL, NULL);
const unsigned long inSize = GetFileSize (in, NULL);
HANDLE inMapping = CreateFileMapping
    (in, NULL, PAGE_READONLY, 0, 0, NULL);
const char *inData = reinterpret_cast<const char *>
    (MapViewOfFile (inMapping, FILE_MAP_READ, 0, 0, 0));

unsigned long lineCount = 0;
unsigned long i;
for (i = 0; i < inSize; ++i)
{
    if (lineCount == desiredLineNumber) break;
    if (inData [i] == '\n') ++lineCount;
}