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As a C programmer, I was surprised to see that wc -c (which count the number of bytes), and wc -m (which counts the number of characters) output very different results for a long, text file of mine. I had always been told that sizeof(char) is 1 byte.

qdii@nomada ~/Documents $ wc -c sentences.csv
102990983 sentences.csv
qdii@nomada ~/Documents $ wc -m sentences.csv
89023123 sentences.csv

Any explanation?

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See @rici's answer below... you've got your -m and -c flags backwards in your question (c = bytes, m = characters)... your example output is correct, though. – Dan Oct 16 '12 at 19:16
@Dan thanks, this is fixed – qdii Oct 16 '12 at 19:51
up vote 18 down vote accepted

The char type in C is one byte, but it's intended for ASCII characters; there are variable-width encodings like UTF-8 that can take up many bytes per character. wc uses the mbrtowc(3) function to decode multibyte sequences, depending on the locale set by the LC_CTYPE environment variable. If you set the locale properly, you should get the same result for all cases. For example:

qdii@nomada ~/Documents $ LC_CTYPE="C" wc -m sentences.csv
102990983 sentences.csv
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At a guess,

  1. Your locale uses UTF-8 encoding, and

  2. About 10% of your file consists of characters which require more than one octet to encode into UTF-8.

By the way, from man wc:

   -c, --bytes
          print the byte counts

   -m, --chars
          print the character counts
share|improve this answer
Thanks for adding correction regarding -m & -c flags. – Dan Oct 16 '12 at 19:15

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