311 lines
9.5 KiB
Markdown
311 lines
9.5 KiB
Markdown
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# cflags
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Command line flag parsing library in C
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Heavily inspired by Go's `flag` package
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https://golang.org/pkg/flag/
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## Building
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cflags is a header only library. To use it, simply copy `cflags.h` or `cflags.hpp` to your project, or add it to your include path.
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You may also install it using cmake, like so:
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```
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cmake path/to/source
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sudo make install
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```
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This will install both CMake and pkg-config configuration files.
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## Argument Parsing Logic
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* The first argument is stored in `program`
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* The following arguments are parsed left to right
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* If an argument does not start with `-`, it is placed in the additional arguments list stored in `args/argv`
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* If the special `--` argument appears, all following arguments are treated as positional
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e.g. `-c 4 -- --name hello` would parse the `-c`, but place `--name` and `hello` into `args/argv`
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* Arguments starting with `--` are long name flags, e.g. `--example`
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* The list of flags is searched for one with `long_name` equal to the argument name (after the `--`), e.g. `long_name == example`
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* If a flag is not found with that name, an error is printed and `parse()` returns false
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* Arguments starting with just `-` are short name flags, e.g. `-xvf`
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* These can be grouped together, so they are searched one at a time from left to right, e.g. `x`, `v`, then `f`
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* If any of these fail to match a flag, an error is printed and `parse()` returns false
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* Once a flag is found, it attempts to find a value
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* Arguments with long names can also come in the forms `--name`, `--name=value`, or `--name value`
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* Arguemnts with short names can come in the forms `-n`, or `-n value`
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* Note: Only the last short flag of a group can have a value, e.g. `-xvf file` will work, but `-xfv file` will fail
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* If the flag is of type `[c]string`, `int`, or `float` then a value is required, and if one is not found an error is printed and `parse()` returns false
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* Arguments of type `bool` can have a value, e.g. `--debug=false`, but one is not required
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* Each time a flag is encountered, the `count` member is incremented
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* The value for a flag is overwritten each time the flag is processed, the last argument parsed wins, e.g. `-c 4 -c 10` will result in `-c` being 10
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* If you want to capture each argument separately, use `add_*_callback` instead
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## Usage (C)
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```cpp
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#include <cflags.h>
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void process_string(const char * str)
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{
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printf("processing %s\n", str);
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}
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void process_bool(bool b)
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{
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printf("processing %d\n", b);
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}
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void process_int(int i)
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{
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printf("processing %d\n", i);
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}
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void process_float(float f)
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{
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printf("processing %f\n", f);
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}
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int main(int argc, char** argv)
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{
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// Create a cflags object
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cflags_t * flags = cflags_init();
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// Add a bool flag, which will be callable with -d or --debug
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// The value will be true if it exists, and can bet set to false
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// by saying -d false or --debug=false
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bool debug = false;
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cflags_add_bool(flags, 'd', "debug", &debug, "enable debug mode");
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// Add a similar help flag, which will be callable with just --help
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bool help = false;
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cflags_add_bool(flags, '\0', "help", &help, "print this text and exit");
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// Add a string flag
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const char * string = NULL;
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cflags_add_string(flags, 's', "string", &string, "enter a string");
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// Add an int flag
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int count = 0;
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cflags_add_int(flags, 'c', "count", &count, "enter a number");
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// Add a float flag
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float amount = 0.f;
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cflags_add_float(flags, 'a', "amount", &amount, "enter a float");
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// Add a string callback flag. This will call the supplied function with the value
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// when it is parsed
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cflags_add_string_callback(flags, 'f', "file", &process_string, "process a file");
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cflags_add_bool_callback(flags, 'q', "bool-flag", &process_bool, "process a bool");
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cflags_add_int_callback(flags, 'w', "int-flag", &process_int, "process a int");
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cflags_add_float_callback(flags, 'e', "float-flag", &process_float, "process a float");
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// Add a flag that can be called multiple times
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cflags_flag_t * verbose = cflags_add_bool(flags, 'v', "verbose", NULL, "enables verbose output, repeat up to 4 times for more verbosity");
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// Parse the command arguments
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if (!cflags_parse(flags, argc, argv) || help || flags->argc == 0) {
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cflags_print_usage(flags,
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"[OPTION]... [ARG]...",
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"Tests the cflags library.",
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"Additional information about this library can be found by at:\n"
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" https://github.com/WhoBrokeTheBuild/cflags");
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}
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printf("debug: %d\n", debug);
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printf("string: %s\n", string);
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printf("count: %d\n", count);
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printf("amount: %f\n", amount);
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// Print the number of times verbose was added
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printf("verbosity: %d\n", verbose->count);
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// Print any additional arguments, in the order they were parsed
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for (int i = 1; i < flags->argc; ++i) {
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printf("positional arg %d: %s\n", i, flags->argv[i]);
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}
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// Cleanup
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cflags_free(flags);
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return 0;
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}
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```
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## Usage (C++)
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```cpp
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#include <cflags.hpp>
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void process_string(std::string str)
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{
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printf("processing %s\n", str.c_str());
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}
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void process_cstring(const char * str)
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{
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printf("processing %s\n", str);
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}
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void process_bool(bool b)
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{
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printf("processing %d\n", b);
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}
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void process_int(int i)
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{
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printf("processing %d\n", i);
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}
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void process_float(float f)
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{
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printf("processing %f\n", f);
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}
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int main(int argc, char * argv[])
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{
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// Create a cflags object
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cflags::cflags flags;
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// Add a bool flag, which will be callable with -d or --debug
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// The value will be true if it exists, and can bet set to false
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// by saying -d false or --debug=false
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bool debug = false;
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flags.add_bool('d', "debug", &debug, "enable debug mode");
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// Add a similar help flag, which will be callable with just --help
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bool help = false;
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flags.add_bool('\0', "help", &help, "print this text and exit");
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// Add a string flag
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std::string string;
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flags.add_string('s', "string", &string, "enter a string");
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// Add a cstring flag
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const char * cstring = NULL;
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flags.add_cstring('\0', "cstring", &cstring, "enter a string (cstring)");
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// Add an int flag
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int count = 0;
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flags.add_int('c', "count", &count, "enter a number");
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// Add a float flag
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float amount = 0.f;
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flags.add_float('a', "amount", &amount, "enter a float");
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// Add a string callback flag. This will call the supplied function with the value
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// when it is parsed
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flags.add_string_callback('f', "file", &process_string, "process a file");
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flags.add_cstring_callback('\0', "cfile", &process_cstring, "process a file (cstring)");
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flags.add_bool_callback('q', "bool-flag", &process_bool, "process a bool");
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flags.add_int_callback('w', "int-flag", &process_int, "process a int");
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flags.add_float_callback('e', "float-flag", &process_float, "process a float");
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// You can also use lambdas
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flags.add_string_callback('l', "lambda",
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[](std::string value) {
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printf("Hello %s\n", value.c_str());
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},
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"use a lambda function"
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);
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// Add a flag that can be called multiple times
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auto verbose = flags.add_bool('v', "verbose", NULL, "enables verbose output, repeat up to 4 times for more verbosity");
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// Parse the command arguments
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if (!flags.parse(argc, argv) || help || flags.argc == 0) {
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flags.print_usage(
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"[OPTION]... [ARG]...",
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"Tests the cflags library.",
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"Additional information about this library can be found by at:\n"
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" https://github.com/WhoBrokeTheBuild/cflags");
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}
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printf("debug: %d\n", debug);
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printf("string: %s\n", string.c_str());
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printf("cstring: %s\n", cstring);
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printf("count: %d\n", count);
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printf("amount: %f\n", amount);
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// Print the number of times verbose was added
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printf("verbosity: %d\n", verbose->count);
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// Print any additional arguments, in the order they were parsed
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for (auto& arg : flags.args) {
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printf("positional arg %s\n", arg.data());
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}
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// For backwards compatability, the additional arguments are also exposed in argc/argv
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for (int i = 0; i < flags.argc; ++i) {
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printf("positional arg %d: %s\n", i, flags.argv[i]);
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}
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return 0;
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}
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```
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## Quirks
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### 1. Only the last short-name argument in a group may have a value.
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For example:
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```cpp
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flags.add_string('f', "file", parse_filename, "parse a filename");
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flags.add_bool('d', "debug", &debug, "enable debug mode");
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// These will work
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test -df test.txt
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test -df test.txt -f test2.txt
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// And these will fail
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test -fd test.txt
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test -ff test.txt test2.txt
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```
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### 2. Any `char *` strings point to the original memory from `argv`
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Call the following code as `program -s hello`
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```cpp
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int main(int argc, char ** argv)
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{
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for (int i = 1; i < argc; ++i) {
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printf("argv[%d] @ %p: %s\n", i, argv[i], argv[i]);
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}
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cflags_t * flags = cflags_init();
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const char * string = NULL;
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cflags_add_string(flags, 's', "string", &string, "enter a string");
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cflags_parse(flags, argc, argv);
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// The address pointed to by `string` is the same memory pointed to by argv
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printf("string @ %p: %s\n", string, string);
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cflags_free(flags);
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return 0;
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}
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```
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Example output
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```
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argv[1] @ 0000024F6BDD665F: -s
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argv[2] @ 0000024F6BDD6662: hello
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string @ 0000024F6BDD6662: hello
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```
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When parsing arguments in the form `--name=value`, the memory pointed to by `argv` is altered and the `=` is replaced by a `\0`.
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When using the C++ version, arguments as `std::string` do not point at `argv` as their memory gets copied.
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