C编程，从文件中读取特定部分

Question

my question is how can I read specific sections from a file? For instance, if my file was: 454545454 Joe Brown 70 50 40 656565656 David Smith 80 90 100 383838383 George Williams 95 100 80

How could I read the first string (9-Digit #), skip over the name, and then read the 3 sets of numbers?

Answer 1

Instead of "reading specific sections," read file line by line and save the information you want and discard the others. scanf is used to read formatted from an external source into program variables. Since scanf returns the number of successful reads from the source, you can use that to do some error checking.

char num_string[STR_LEN];
int numbers[3];
char dummy1[STR_LEN], dummy2[STR_LEN];
int num_read = scanf( "%s%s%s%d%d%d", num_string, dummy1, dummy2, &numbers[0], &numbers[1], &numbers[2] );

if( num_read != 6 )
    // error
else
{
    // do stuff with num_string, and numbers[0]-numbers[2]
}

Answer 2

I think that you could notice that the white space is your sentinel. I'm thinking that maybe you can store the whole file into a char* and asking for this sentinel each time. Other solution could be using atoi (ascii to int) for validate if it's a number or a letter. You can also read about fread and fseek .

I think that the best way is to mix both solution... find each sentinel and try to parse it using atoi.

The main idea is that you try to find some pattern in the file that allows you to think the algorithm. In C, most of the times you have to solve the logic by yourself.

Hope it helps!