Reading in scientific notation from C++ to Mathematica

Similar to Rolf's method:

string = "f[38.67]=-2.5387862698183892298317350539374412777263289550697e-05;";

StringReplace[string, {"e+" :> "*^", "e-" :> "*^-"}];

ToExpression@%;

?? f

Global`f

f[38.67] = -0.000025387862698183892298317350539374412777263289550697

Depending on your data you may want a more specific pattern, e.g.:

StringReplace[string,
  {a : NumberString ~~ "e" ~~ b : NumberString :> a <> "*^" <> b}]

Import usually automatically converts the e format to powers of. You can use ImportString with the "Table" or "List" type:

ImportString["-2.5387862698183892298317350539374412777263289550697e-05", "Table"]

{{-0.000025387862698183892298317350539374412777263289550697}}

or

ImportString["1.002e-26", "Table"]

{{1.002*10^-26}}

For those wishing to transform a full data file with numbers in scientific notation that is output from Fortran (or C, et al.) as "1.6E-19" and "3.0E+08" and such, it is incredibly faster to make changes in the Unix sed command line editor than doing a search and replace in the .m file within Mathematica or any word processor. At the Unix prompt $ one types

$ cat FilewE.m | sed 's/E-/*^-/g' | sed 's/E+/*^+/g' > FilewoE.m

For those new to Unix, the cat command "concatenates" a single file (named FilewE.m in this example), which normally would flow the contents onto the terminal screen. Instead the flow is piped | into sed and, to avoid killing off any Es that appear in words, E- is replaced with *^- globally g. The output of that is piped into sed again to catch the positive exponents and the output of that is directed > to the output file named FilewoE.m in this example.