StokeBloke.com

Well I thought I would write about an issue I have known about for some time, but it appears others still dont.

Its regarding stdio fgetc() performance. Mainly that using fgetc() is always slow and should rarely be used.

Here is a comparison of fgetc(), fread() and fgets() when reading a 333Mb mbox file created via thunderbird.

Times are take on a quad core 2.4Ghz (linux 2.6.2.4 tuxonice r4 gentoo)

The performance issues clear show that retrieving information in larger ‘chunks’ is more efficient and its scary how different the performance is. Unless you only want 1 or a few characters, you should probably not use getc()

The code

fgetc()

clock_t start;
clock_t end;
FILE* testFile;
char buf[8*1024];
unsigned char chr;

testFile = fopen("testdata", "r");
start = clock();
    
while(!feof(testFile)) {
    chr = (unsigned char)getc(testFile);
}

end = clock();
printf("fgetc() %f seconds\n", ((float)end - (float)start) / (float)CLOCKS_PER_SEC);

fgets()

clock_t start;
clock_t end;
FILE* testFile;
char buf[8*1024];

testFile = fopen("testdata", "r"); 
start = clock();

do {}  while (fgets (buf, sizeof(buf), testFile) != NULL);

end = clock();
printf("fgets() %f seconds\n", ((float)end - (float)start) / (float)CLOCKS_PER_SEC);

fread()

clock_t start;
clock_t end;
FILE* testFile;
char data[8*1024];
int r = 1;

testFile = fopen("testdata", "r");
start = clock();
    
while(r!=0) {
    r = fread(data, sizeof(char), 1024*8, testFile);
}
    
end = clock();
printf("fread() %f seconds\n", ((float)end - (float)start) / (float)CLOCKS_PER_SEC);

This entry was posted on Tuesday, April 15th, 2008 at 1:32 pm and is filed under Programming. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.