What is the easiest way to count the newlines in an ASCII file?

by

Normally you read files in C using fgets. You can also use scanf("%[^\n]"), but quite a few people reading the code are likely to find that confusing and foreign.

Edit: on the other hand, if you really do just want to count lines, a slightly modified version of the scanf approach can work quite nicely:

while (EOF != (scanf("%*[^\n]"), scanf("%*c"))) 
    ++lines;

The advantage of this is that with the ‘*’ in each conversion, scanf reads and matches the input, but does nothing with the result. That means we don’t have to waste memory on a large buffer to hold the content of a line that we don’t care about (and still take a chance of getting a line that’s even larger than that, so our count ends up wrong unless we got to even more work to figure out whether the input we read ended with a newline).

Unfortunately, we do have to break up the scanf into two pieces like this. scanf stops scanning when a conversion fails, and if the input contains a blank line (two consecutive newlines) we expect the first conversion to fail. Even if that fails, however, we want the second conversion to happen, to read the next newline and move on to the next line. Therefore, we attempt the first conversion to “eat” the content of the line, and then do the %c conversion to read the newline (the part we really care about). We continue doing both until the second call to scanf returns EOF (which will normally be at the end of the file, though it can also happen in case of something like a read error).

Edit2: Of course, there is another possibility that’s (at least arguably) simpler and easier to understand:

int ch;

while (EOF != (ch=getchar()))
    if (ch=='\n')
        ++lines;

The only part of this that some people find counterintuitive is that ch must be defined as an int, not a char for the code to work correctly.

More Related Contents:

  1. while loop and static variable
  2. Why is a=4 evaluated as true but b=0 evaluated as false in an if condition?
  3. Given an executable file, display its complete path [closed]
  4. What is the behavior of integer division?
  5. How do function pointers in C work?
  6. Undefined reference to pthread_create in Linux
  7. sizeof() operator in if-statement
  8. close vs shutdown socket?
  9. What does void* mean and how to use it?
  10. What is the reason for using a double pointer when adding a node in a linked list?
  11. Can the linker inline functions?
  12. using rand to generate a random numbers
  13. How to compare pointer to strings in C
  14. How to share semaphores between processes using shared memory
  15. How to make weak linking work with GCC?
  16. File Operations in Android NDK
  17. Share condition variable & mutex between processes: does mutex have to locked before?
  18. How to clear stdin before getting new input?
  19. Convert a Static Library to a Shared Library?
  20. gcc, strict-aliasing, and casting through a union
  21. Accessing elements of a matrix row-wise versus column-wise
  22. What does “request for member ‘*******’ in something not a structure or union” mean?
  23. behaviour of malloc(0)
  24. Arrow Operator vs. Dot Operator [closed]
  25. Compiling multiple C files in a program
  26. How do I debug the child process after fork() in gdb?
  27. How do you check if a directory exists on Windows in C?
  28. Returning struct containing array
  29. C Function to Convert float to byte array
  30. Efficient way to find task_struct by pid

Leave a Comment