Wouldn't it be a mess of single quotes and double quotes?

No. For the reasons I already gave, it would be less of a mess in Perl.

Perl:
print($fh q{for (keys(%h)) { print("$_: $h{$k}\n"); }});

C:
fprintf(fh, "for (keys(%%h)) { print(\"$_: $h{$_}\\n\"); }");
fprintf(fh, "%s", "for (keys(%h)) { print(\"$_: $h{$_}\\n\"); }");
fputs("for (keys(%h)) { print(\"$_: $h{$_}\\n\"); }", fh);
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3 or 4 extra escapes in C.