C++实现的命令行参数管理
在编写可运行程序时，经常需要输入除了可运行文件之外的其它的命令行参数，可以用传统的getopt函数来分析，本文基于面向对象，分析一种管理命令行参数方法 -- 来源于webrtc项目，在阅读过程中，大家分享一下。
一，传统命令行分析
#include <stdio.h>#include <stdlib.h>#include <string.h>#ifdef WIN32#include "talk/base/win32.h"#include <shellapi.h>#endif#include "talk/base/flags.h"// -----------------------------------------// Implementation of FlagFlag::Flag(const char* file, const char* name, const char* comment, Type type, void* variable, FlagValue default__) : file_(file), name_(name), comment_(comment), type_(type), variable_(reinterpret_cast<FlagValue*>(variable)), default_(default__) { FlagList::Register(this);}void Flag::SetToDefault() { // Note that we cannot simply do '*variable_ = default_;' since // flag variables are not really of type FlagValue and thus may // be smaller! The FlagValue union is simply 'overlayed' on top // of a flag variable for convenient access. Since union members // are guarantee to be aligned at the beginning, this works. switch (type_) { case Flag::BOOL: variable_->b = default_.b; return; case Flag::INT: variable_->i = default_.i; return; case Flag::FLOAT: variable_->f = default_.f; return; case Flag::STRING: variable_->s = default_.s; return; } UNREACHABLE();}static const char* Type2String(Flag::Type type) { switch (type) { case Flag::BOOL: return "bool"; case Flag::INT: return "int"; case Flag::FLOAT: return "float"; case Flag::STRING: return "string"; } UNREACHABLE(); return NULL;}static void PrintFlagValue(Flag::Type type, FlagValue* p) { switch (type) { case Flag::BOOL: printf("%s", (p->b ? "true" : "false")); return; case Flag::INT: printf("%d", p->i); return; case Flag::FLOAT: printf("%f", p->f); return; case Flag::STRING: printf("%s", p->s); return; } UNREACHABLE();}void Flag::Print(bool print_current_value) { printf(" --%s (%s) type: %s default: ", name_, comment_, Type2String(type_)); PrintFlagValue(type_, &default_); if (print_current_value) { printf(" current value: "); PrintFlagValue(type_, variable_); } printf("\n");}// -----------------------------------------// Implementation of FlagListFlag* FlagList::list_ = NULL;FlagList::FlagList() { list_ = NULL;}void FlagList::Print(const char* file, bool print_current_value) { // Since flag registration is likely by file (= C++ file), // we don't need to sort by file and still get grouped output. const char* current = NULL; for (Flag* f = list_; f != NULL; f = f->next()) { if (file == NULL || file == f->file()) { if (current != f->file()) { printf("Flags from %s:\n", f->file()); current = f->file(); } f->Print(print_current_value); } }}Flag* FlagList::Lookup(const char* name) { Flag* f = list_; while (f != NULL && strcmp(name, f->name()) != 0) f = f->next(); return f;}void FlagList::SplitArgument(const char* arg, char* buffer, int buffer_size, const char** name, const char** value, bool* is_bool) { *name = NULL; *value = NULL; *is_bool = false; if (*arg == '-') { // find the begin of the flag name arg++; // remove 1st '-' if (*arg == '-') arg++; // remove 2nd '-' if (arg[0] == 'n' && arg[1] == 'o') { arg += 2; // remove "no" *is_bool = true; } *name = arg; // find the end of the flag name while (*arg != '\0' && *arg != '=') arg++; // get the value if any if (*arg == '=') { // make a copy so we can NUL-terminate flag name int n = static_cast<int>(arg - *name); if (n >= buffer_size) Fatal(__FILE__, __LINE__, "CHECK(%s) failed", "n < buffer_size"); memcpy(buffer, *name, n * sizeof(char)); buffer[n] = '\0'; *name = buffer; // get the value *value = arg + 1; } }}int FlagList::SetFlagsFromCommandLine(int* argc, const char** argv, bool remove_flags) { // parse arguments for (int i = 1; i < *argc; /* see below */) { int j = i; // j > 0 const char* arg = argv[i++]; // split arg into flag components char buffer[1024]; const char* name; const char* value; bool is_bool; SplitArgument(arg, buffer, sizeof buffer, &name, &value, &is_bool); if (name != NULL) { // lookup the flag Flag* flag = Lookup(name); if (flag == NULL) { fprintf(stderr, "Error: unrecognized flag %s\n", arg); return j; } // if we still need a flag value, use the next argument if available if (flag->type() != Flag::BOOL && value == NULL) { if (i < *argc) { value = argv[i++]; } else { fprintf(stderr, "Error: missing value for flag %s of type %s\n", arg, Type2String(flag->type())); return j; } } // set the flag char empty[] = { '\0' }; char* endp = empty; switch (flag->type()) { case Flag::BOOL: *flag->bool_variable() = !is_bool; break; case Flag::INT: *flag->int_variable() = strtol(value, &endp, 10); break; case Flag::FLOAT: *flag->float_variable() = strtod(value, &endp); break; case Flag::STRING: *flag->string_variable() = value; break; } // handle errors if ((flag->type() == Flag::BOOL && value != NULL) || (flag->type() != Flag::BOOL && is_bool) || *endp != '\0') { fprintf(stderr, "Error: illegal value for flag %s of type %s\n", arg, Type2String(flag->type())); return j; } // remove the flag & value from the command if (remove_flags) while (j < i) argv[j++] = NULL; } } // shrink the argument list if (remove_flags) { int j = 1; for (int i = 1; i < *argc; i++) { if (argv[i] != NULL) argv[j++] = argv[i]; } *argc = j; } // parsed all flags successfully return 0;}void FlagList::Register(Flag* flag) { assert(flag != NULL && strlen(flag->name()) > 0); if (Lookup(flag->name()) != NULL) Fatal(flag->file(), 0, "flag %s declared twice", flag->name()); flag->next_ = list_; list_ = flag;}#ifdef WIN32WindowsCommandLineArguments::WindowsCommandLineArguments() { // start by getting the command line. LPTSTR command_line = ::GetCommandLine(); // now, convert it to a list of wide char strings. LPWSTR *wide_argv = ::CommandLineToArgvW(command_line, &argc_); // now allocate an array big enough to hold that many string pointers. argv_ = new char*[argc_]; // iterate over the returned wide strings; for(int i = 0; i < argc_; ++i) { std::string s = talk_base::ToUtf8(wide_argv[i], wcslen(wide_argv[i])); char *buffer = new char[s.length() + 1]; talk_base::strcpyn(buffer, s.length() + 1, s.c_str()); // make sure the argv array has the right string at this point. argv_[i] = buffer; } LocalFree(wide_argv);}WindowsCommandLineArguments::~WindowsCommandLineArguments() { // need to free each string in the array, and then the array. for(int i = 0; i < argc_; i++) { delete[] argv_[i]; } delete[] argv_;}#endif // WIN32