How to calculate the number of lines in a file?
I am working in C language for the first time and wondering.
How can I get the number of lines in a file?
FILE *in;
char c;
int lines = 1;
...
while (fscanf(in,"%c",&c) == 1) {
if (c == '\n') {
lines++;
}
}
I'm right? I don't really know how to get the moment when the line crosses the newline.
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The OP code works well, except maybe the issue released separately and the last line issue.
C library standard definition
A text stream is an ordered sequence of characters arranged in lines, each line consisting of zero or more characters plus a terminating newline character. Whether the last line matches a trailing newline is implementation-defined. C11dr §7.21.2 2
The line ends with '\n'
, and the last line may or may not end with '\n
'.
If you are using the idea that no final is required for the last line of a file '\n
, then the goal is to count the number of occurrences that a character reads after '\n'
.
// Let us use a wide type
// Start at 0 as the file may be empty
unsigned long long line_count = 0;
int previous = '\n';
int ch;
while ((ch = fgetc(in)) != EOF) {
if (previous == '\n') line_count++;
previous = ch;
}
printf("Line count:%llu\n", line_count);
Reading a file one character at a time may be less efficient than other means, but functionally suits the OP's purpose.
This answer uses (ch = fgetc(in)) != EOF
instead fscanf(in,"%c",&c) == 1
, which is generally "faster", but with an optimizing compiler, or can generate similar performance code. Such speed details can be supported by analysis or profiling., Code for clarity.
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Can use this utility function
/*
* count the number of lines in the file called filename
*
*/
int countLines(char *filename)
{
FILE *in = fopen(filename,"r");
int ch=0;
int lines=0;
if(in == NULL){
return 0; // return lines;
}
while((ch = fgetc(in)) != EOF){
if(ch == '\n'){
lines++;
}
}
fclose(in);
return lines;
}
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When counting the number of characters \n
, you must remember that you are counting separators, not elements. See ' Fencepost error
Your example should work, but:
- If the file doesn't end with
\n
, then you might be fine (depending on your definition of "string"). - depending on your definition of "string" you may be missing
\r
characters in the file (typically used by Mac) - it won't be very efficient or fast (the call is
scanf()
expensive)
The example below will load the buffer each time, looking for characters \r
and \n
. There is some logic to latch these characters, so the following lines need to be handled correctly:
-
\n
-
\r
-
\r\n
#include <stdio.h>
#include <errno.h>
int main(void) {
FILE *in;
char buf[4096];
int buf_len, buf_pos;
int line_count, line_pos;
int ignore_cr, ignore_lf;
in = fopen("my_file.txt", "rb");
if (in == NULL) {
perror("fopen()");
return 1;
}
line_count = 0;
line_pos = 0;
ignore_cr = 0;
ignore_lf = 0;
/* ingest a buffer at a time */
while ((buf_len = fread(&buf, 1, sizeof(buf), in)) != 0) {
/* walk through the buffer, looking for newlines */
for (buf_pos = 0; buf_pos < buf_len; buf_pos++) {
/* look for '\n' ... */
if (buf[buf_pos] == '\n') {
/* ... unless we've already seen '\r' */
if (!ignore_lf) {
line_count += 1;
line_pos = 0;
ignore_cr = 1;
}
/* look for '\r' ... */
} else if (buf[buf_pos] == '\r') {
/* ... unless we've already seen '\n' */
if (!ignore_cr) {
line_count += 1;
line_pos = 0;
ignore_lf = 1;
}
/* on any other character, count the characters per line */
} else {
line_pos += 1;
ignore_lf = 0;
ignore_cr = 0;
}
}
}
if (line_pos > 0) {
line_count += 1;
}
fclose(in);
printf("lines: %d\n", line_count);
return 0;
}
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