genproto

If you're looking for a tool that can generate prototypes from C/C++ code, then you may want to consider genproto. With this software, you don't have to worry about it touching your original files. Additionally, you can easily change the output format using printf-style format strings.

One advantage of using genproto over another similar software, cproto, is that it doesn't require external programs (such as gcc or cpp).

Here's an example of how genproto can be used:
me@home:~/src/genproto-0.2> ./genproto main.c
/* generated by genproto */
void Usage(char *name);
char * CharCopy(char *buf, int len);
char * AddTokens(char **TokenList, int FirstToken, int LastToken);
void AddPrototype(char **TokenList, int ClassNamePos, int FunctionNamePos, int ParamPos);
void ScanOneFile(void);
void SortPrototypes(struct function **T, int Gauche, int Droite);
void Swap(struct function **T, int i, int j);
int CompareFunctions(struct function *pF1, struct function *pF2);
void CopyListToTable(void);
void PrintOnePrototype(struct function *pF);
void PrintPrototypes(void);
void DeletePrototypes(void);
void MyExit(void);
void * MyAlloc(size_t size);
int main(int argc, char **argv);

Overall, genproto seems to be a useful and efficient tool for generating prototypes. It's user-friendly and doesn't require you to install any external programs. So, if you're in need of a program that can help with generating prototypes from your C/C++ code, give genproto a try.