I used TakeFive Software's SNiFF+ (TakeFive has been bought by WindRiver) for navigating C code. The software was fenomenal and very easy to use. Right-clicking any function/variable name gives you option to see where it is defined and all the places it is used. So it was very easy to jump from file to file. SNiFF+ also creates diagrams showing calls and such. I remember the package being costly, but definitely worth if you have a lot strange code to read.
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I used TakeFive Software's SNiFF+ (TakeFive has been bought by WindRiver) for navigating C code. The software was fenomenal and very easy to use. Right-clicking any function/variable name gives you option to see where it is defined and all the places it is used. So it was very easy to jump from file to file. SNiFF+ also creates diagrams showing calls and such. I remember the package being costly, but definitely worth if you have a lot strange code to read.