I've got this url encoder I found on the internet and made few small changes, however when ever I do something such as this:
char encodedWord[100];
const char* word = "Stack\nOverflow";
urlencode(encodedWord, word);
The output would be something like this:
"Stack0X8.51EE00001674P-1022Overflow" instead of x0A in between of Stack Overflow.
Why is it outputting that? I assume because of the "EE0000" part something went wrong with the char to number conversion.
How can I get my encoder to be much more friendly to special characters? i.e "\n,\r,\r".
The Function
int urlencode(char *dest, const char *src)
{
/* urlencode all non-alphanumeric characters in the C-string 'src'
store result in the C-string 'dest'
return the length of the url encoded C-string
*/
char *d;
int i;
for(i=0, d=dest; src[i]; i++) {
if(isalnum(src[i]) || isdigit(src[i])) {
*(d++) = src[i];
} else {
snprintf(d, 4, "%%%02X", src[i]);
d += 3;
}
}
*d = 0;
return d-dest;
}
System
Windows 10 32bit
Mingw32 (gcc 5.1.0)
Make File
#OBJS specifies which files to compile as part of the project
OBJS = $(wildcard ./src/*.c)
#CC specifies which compiler we're using
CC = gcc
#INCLUDE_PATHS specifies the additional include paths we'll need
INCLUDE_PATHS =
#LIBRARY_PATHS specifies the additional library paths we'll need
LIBRARY_PATHS =
#COMPILER_FLAGS specifies the additional compilation options we're using
# -w suppresses all warnings
# -Wl,-subsystem,windows gets rid of the console window
COMPILER_FLAGS = -Wall -Wl,-subsystem,console -std=c99
#LINKER_FLAGS specifies the libraries we're linking against
LINKER_FLAGS = -lmingw32 -lws2_32 -lwininet -s -lshlwapi
#OBJ_NAME specifies the name of our executable
OBJ_NAME = project
#This is the target that compiles our executable
all : clean build
build:
cls
$(CC) $(OBJS) $(INCLUDE_PATHS) $(LIBRARY_PATHS) $(COMPILER_FLAGS) $(LINKER_FLAGS) -o $(OBJ_NAME)
clean:
del -f $(OBJ_NAME).exe
the urlencode function is working just fine, the problem is how you're printing the output. I was in the middle of writing
0X8.51EE00001674P-1022 is a hexadecimal floating point number, what you would expect to see from a %A printf specifier.
when it struck me that the correct output has %0A in that exact position. Which means that you're making the mistake of passing a non-constant string as the first parameter of printf. Don't do printf(encodedWord); you should be using printf("%s", encodedWord) instead.
Related
I have a problem with my 32-bit protected mode OS project Sinatra. I can compile sources to object files, but I don't know how to link these together. I use NASM and TDM-GCC on Windows. I have fixed problems with my code so it compiles. I have removed the comments for brevity.
My file boot.asm:
[BITS 32]
[global start]
[extern _JlMain]
start:
cli
call _JlMain
hlt
My file JSinatra.h:
#ifndef __SINATRA_H__
#define __SINATRA_H__
#define JWhiteText 0x07
void JlMain();
void JlClearScreen();
unsigned int JlPrintF(char * message, unsigned int line);
#endif
My file JSinatra.c:
#include "JSinatra.h"
void JlClearScreen() // clear entire screen
{
char * vidmem = (char * ) 0xb8000;
unsigned int i = 0;
while (i < (80 * 25 * 2)) {
vidmem[i] = ' ';
i += 1;
vidmem[i] = JWhiteText;
i += 1;
}
}
unsigned int JlPrintF(char * message, unsigned int line) {
char * vidmem = (char * ) 0xb8000;
unsigned int i = 0;
i = line * 80 * 2;
while ( * message != 0) {
if ( * message == '\n') {
line += 1;
i = (line * 80 * 2); * message += 1;
} else {
vidmem[i] = * message; * message += 1;
i += 1;
vidmem[i] = JWhiteText;
i += 1;
}
}
return (1);
}
void JlMain() {
JlClearScreen();
JlPrintF("Sinatra v0 Virgin/Kernel Mode\n", 0);
}
I need to load my OS starting at absolute address 0x100000. How can I properly compile and link my code to create a binary image?
First of all, if you're compiling to ELF, then you mustn't add an initial underscore before functions in assembly.
Now, in order to link different source files together, you obviously have to get them to common ground, which is in this case, object code.
So, what you'll do is:
Assemble the assembly source files to object code.
Compile but not link C source files to object code. In gcc: gcc -c file.c -o file.o
Link those together. In gcc: gcc cfile.o asfile.o -o app
Using GCC-TDM and NASM on Windows
Because you are targeting an OS being loaded at an absolute address without C-runtimes you'll need to make sure you compile as freestanding code; that your asm and C files target the same type of object (win32/PECOFF); and the last step will be converting the PECOFF file to a binary image.
To compile C files you would use something like:
gcc -m32 -ffreestanding -c JSinatra.c -o JSinatra.o
To assemble the asm files you would use something like:
nasm -f win32 boot.asm -o boot.o
To link them together you have to do it in two steps:
ld -m i386pe -T NUL -o sinatra.tmp -Ttext 0x100000 boot.o JSinatra.o
The ld command above will create a temporary file sinatra.tmp that is a 32-bit PECOFF executable. You then need to convert sinatra.tmp to a binary image with a command like:
objcopy -O binary sinatra.tmp sinatra.img
You should then have a binary image in the file sinatra.img
Hello I am completely new to the world of programming an I am attempting to take Harvard's CS50 course online.
While making my "Hello World" program, I downloaded 'cs50.h' to define GetString and string (at least I think). So this is the code I wrote:
file.c:
#include "cs50.h"
#include <stdio.h>
int main(int argc, string argv[])
{
string name;
printf("Enter your name: ");
name = GetString();
printf("Hello, %s\n", name);
}
However, whenever I try to make file, this happens:
cc file.c -o file
Undefined symbols for architecture x86_64:
"_GetString", referenced from:
_main in file-JvqYUC.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [file] Error 1
Here is a link to the cs50.h file if it can help: http://dkui3cmikz357.cloudfront.net/library50/c/cs50-library-c-3.0/cs50.h
I would like to know why I get this error and how I can fix it. Please help.
It seems that you forgot to download and link to project cs50.c file from http://dkui3cmikz357.cloudfront.net/library50/c/cs50-library-c-3.0/cs50.c
*.h usually contain only declarations. *.c (for C) and *.cpp (for C++) contains implementations.
There is GetSting function implementation from this class:
string GetString(void)
{
// growable buffer for chars
string buffer = NULL;
// capacity of buffer
unsigned int capacity = 0;
// number of chars actually in buffer
unsigned int n = 0;
// character read or EOF
int c;
// iteratively get chars from standard input
while ((c = fgetc(stdin)) != '\n' && c != EOF)
{
// grow buffer if necessary
if (n + 1 > capacity)
{
// determine new capacity: start at 32 then double
if (capacity == 0)
capacity = 32;
else if (capacity <= (UINT_MAX / 2))
capacity *= 2;
else
{
free(buffer);
return NULL;
}
// extend buffer's capacity
string temp = realloc(buffer, capacity * sizeof(char));
if (temp == NULL)
{
free(buffer);
return NULL;
}
buffer = temp;
}
// append current character to buffer
buffer[n++] = c;
}
// return NULL if user provided no input
if (n == 0 && c == EOF)
return NULL;
// minimize buffer
string minimal = malloc((n + 1) * sizeof(char));
strncpy(minimal, buffer, n);
free(buffer);
// terminate string
minimal[n] = '\0';
// return string
return minimal;
}
Look at your first include statement. You are using " " instead of < >.
In the videos with the CS50 course, the instructor uses carets (< >) rather than quotation marks (" ").
For anyone taking the CS50 class, and don't want to paste the .c code every time, you can also link the CS50 code when compiling.
Place cs50.h and cs50.c in the same directory as file.c, and then type the following in the command line:
clang file.c -lcs50 -o <file name>
The "-l" links the cs50.c and cs50.h files to your c file (after compiling to object file), and "-o" specifies where to put the compiled output.
More information on this here
In your #include"cs50.h" header you should be typing it like this: #include<cs50.h>. Also, try doing:
#include<cs50.h>
#include<stdio.h>
int main(void)
{
string name = get_string("Enter your name: ");
printf("%s\n", name);
}
Instead of this:
#include "cs50.h"
#include <stdio.h>
int main(int argc, string argv[])
{
string name;
printf("Enter your name: ");
name = GetString();
printf("Hello, %s\n", name);
}
That should get rid of the error messages.
P.S
In week 2 they tell you about help50, but if you want you can use it now.
I myself have found it very useful. Here's how it works: in your terminal window(the one where you execute ./hello and clang) you should type : "help50 make hello" (without the quotation marks) and then it will type: asking for help... in yellow. Then it will decipher the error message and type it in a more simple language. For example:
#include <stdio.h>
#include <cs50.h>
int main(void)
{
string name = get_string("Enter your name: ");
printf("%s\n", name)
}
I do make hello, and this appears:
clang -ggdb3 -O0 -std=c11 -Wall -Werror -Wextra -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wshadow hello.c -lcrypt -lcs50 -lm -o hello
hello.c:13:21: error: expected ';' after expression
printf("%s\n", name)
^
;
1 error generated.
<builtin>: recipe for target 'hello' failed
make: *** [hello] Error 1
But when I do it with help50 make hello, this appears:
clang -ggdb3 -O0 -std=c11 -Wall -Werror -Wextra -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wshadow hello.c -lcrypt -lcs50 -lm -o hello
hello.c:13:21: error: expected ';' after expression
printf("%s\n", name)
^
;
1 error generated.
<builtin>: recipe for target 'hello' failed
make: *** [hello] Error 1
Asking for help...
hello.c:13:21: error: expected ';' after expression
printf("%s\n", name)
^
;
Are you missing a semicolon at the end of line 13 of hello.c?
As you can see, now I know my problem and can fix it. Help50 deciphers the error messages into a language you can understand.
I am trying to execute a PintOS command pintos -f (do not worry if you are not familiar with PintOS). Internally, init.c program is called, whose parse_options() function handles the command line arguments passed. Below is the relevant snippet of init.c
static char **
parse_options (char **argv)
{
for (; *argv != NULL && **argv == '-'; argv++)
{
char *save_ptr;
char *name = strtok_r (*argv, "=", &save_ptr); //fn to tokenise the string
char *value = strtok_r (NULL, "", &save_ptr);
if (!strcmp (name, "-h"))
usage ();
else if (!strcmp (name, "-q"))
power_off_when_done = true;
else if (!strcmp (name, "-r"))
reboot_when_done = true;
/*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*/
#ifdef FILESYS
else if (!strcmp (name, "-f"))
format_filesys = true;
#endif
/*$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$*/
else if (!strcmp (name, "-rs"))
random_init (atoi (value));
else if (!strcmp (name, "-mlfqs"))
thread_mlfqs = true;
#ifdef USERPROG
else if (!strcmp (name, "-ul"))
user_page_limit = atoi (value);
#endif
else
PANIC ("unknown option `%s' (use -h for help)", name);
}
return argv;
}
As per the code inside the $$$$ section, the -f option passed will be processed only if FILESYS is defined.
On executing make, the following command is executed
gcc -m32 -c ../../threads/init.c -o threads/init.o -g -msoft-float -O -fno-stack- protector -nostdinc -I../.. -I../../lib -I../../lib/kernel -Wall -W -Wstrict-prototypes -Wmissing-prototypes -Wsystem-headers -DUSERPROG -DFILESYS -MMD -MF threads/init.d
Here, -DUSERPROG and -DFILESYS options are provided to define FILESYS and USERPROG, so that the relevant sections of the code can be executed. However, somehow, FILESYS is not getting defined, as evident from the following output of pintos -f command
Kernel command line: -f
Kernel PANIC at ../../threads/init.c:261 in parse_options(): unknown option `-f' (use -h for help)
Several other tests confirm that FILESYS not getting defined IS the issue. I checked the gcc syntax and even wrote the following Dummy program to check the -DNAME option with gcc.
DummyProg.c
#include "stdio.h"
int main()
{
#ifdef CHECK
printf("WORKING\n");
#endif
return 0;
}
With gcc -DCHECK DummyProg.c and ./a.out, WORKING was displayed on the screen, conforming the validity of syntax etc. The gcc version I am using is gcc (Ubuntu/Linaro 4.7.3-1ubuntu1) 4.7.3
Could someone please point how to resolve this issue.
The compiler can help you understand this; the trick is to capture the proprocessed code with the #define statements left in:
gcc -E -dD ...blah...
You have to remove the -c and -o <outfile> options from the compile command, but otherwise leave it unchanged, apart from adding the two new options.
-E tells it to do the preprocess step only, and output it to screen.
-dD tells it to leave in the #define and #undef directives.
My guess is that your code has a #undef FILESYS directive somewhere, and it's overriding your -DFILESYS option.
To debug issues like this, run gcc with -E. This will just run the code through the preprocessor cpp. Look into the output file to see what the input of the C compiler would be after the post-processing step.
are you sure you are building the entire executable/library/...?
looking at the command that gets triggered when calling make, only a single file is compiled into an intermediate object file. no linking into the final binary happens.
so it guess that you are still using an outdated build. try going to the toplevel source directory and execute:
make clean && make
I have a linux C program that handles request sent to a TCP socket (bound to a particular port). I want to be able to query the internal state of the C program via a request to that port, but I dont want to hard code what global variables can be queried. Thus I want the query to contain the string name of a global and the C code to look that string up in the symbol table to find its address and then send its value back over the TCP socket. Of course the symbol table must not have been stripped. So can the C program even locate its own symbol table, and is there a library interface for looking up symbols given their name? This is an ELF executable C program built with gcc.
This is actually fairly easy. You use dlopen / dlsym to access symbols. In order for this to work, the symbols have to be present in the dynamic symbol table. There are multiple symbol tables!
#include <dlfcn.h>
#include <stdio.h>
__attribute__((visibility("default")))
const char A[] = "Value of A";
__attribute__((visibility("hidden")))
const char B[] = "Value of B";
const char C[] = "Value of C";
int main(int argc, char *argv[])
{
void *hdl;
const char *ptr;
int i;
hdl = dlopen(NULL, 0);
for (i = 1; i < argc; ++i) {
ptr = dlsym(hdl, argv[i]);
printf("%s = %s\n", argv[i], ptr);
}
return 0;
}
In order to add all symbols to the dynamic symbol table, use -Wl,--export-dynamic. If you want to remove most symbols from the symbol table (recommended), set -fvisibility=hidden and then explicitly add the symbols you want with __attribute__((visibility("default"))) or one of the other methods.
~ $ gcc dlopentest.c -Wall -Wextra -ldl
~ $ ./a.out A B C
A = (null)
B = (null)
C = (null)
~ $ gcc dlopentest.c -Wall -Wextra -ldl -Wl,--export-dynamic
~ $ ./a.out A B C
A = Value of A
B = (null)
C = Value of C
~ $ gcc dlopentest.c -Wall -Wextra -ldl -Wl,--export-dynamic -fvisibility=hidden
~ $ ./a.out A B C
A = Value of A
B = (null)
C = (null)
Safety
Notice that there is a lot of room for bad behavior.
$ ./a.out printf
printf = ▯▯▯▯ (garbage)
If you want this to be safe, you should create a whitelist of permissible symbols.
file: reflect.c
#include <stdio.h>
#include "reflect.h"
struct sym_table_t gbl_sym_table[1] __attribute__((weak)) = {{NULL, NULL}};
void * reflect_query_symbol(const char *name)
{
struct sym_table_t *p = &gbl_sym_table[0];
for(; p->name; p++) {
if(strcmp(p->name, name) == 0) {
return p->addr;
}
}
return NULL;
}
file: reflect.h
#include <stdio.h>
struct sym_table_t {
char *name;
void *addr;
};
void * reflect_query_symbol(const char *name);
file: main.c
just #include "reflect.h" and call reflect_query_symbol
example:
#include <stdio.h>
#include "reflect.h"
void foo(void)
{
printf("bar test\n");
}
int uninited_data;
int inited_data = 3;
int main(int argc, char *argv[])
{
int i;
void *addr;
for(i=1; i<argc; i++) {
addr = reflect_query_symbol(argv[i]);
if(addr) {
printf("%s lay at: %p\n", argv[i], addr);
} else {
printf("%s NOT found\n", argv[i], addr);
}
}
return 0;
}
file:Makefile
objs = main.o reflect.o
main: $(objs)
gcc -o $# $^
nm $# | awk 'BEGIN{ print "#include <stdio.h>"; print "#include \"reflect.h\""; print "struct sym_table_t gbl_sym_table[]={" } { if(NF==3){print "{\"" $$3 "\", (void*)0x" $$1 "},"}} END{print "{NULL,NULL} };"}' > .reflect.real.c
gcc -c .reflect.real.c -o .reflect.real.o
gcc -o $# $^ .reflect.real.o
nm $# | awk 'BEGIN{ print "#include <stdio.h>"; print "#include \"reflect.h\""; print "struct sym_table_t gbl_sym_table[]={" } { if(NF==3){print "{\"" $$3 "\", (void*)0x" $$1 "},"}} END{print "{NULL,NULL} };"}' > .reflect.real.c
gcc -c .reflect.real.c -o .reflect.real.o
gcc -o $# $^ .reflect.real.o
The general term for this sort of feature is "reflection", and it is not part of C.
If this is for debugging purposes, and you want to be able to inspect the entire state of a C program remotely, examine any variable, start and stop its execution, and so on, you might consider GDB remote debugging:
GDB offers a 'remote' mode often used when debugging embedded systems.
Remote operation is when GDB runs on one machine and the program being
debugged runs on another. GDB can communicate to the remote 'stub'
which understands GDB protocol via Serial or TCP/IP. A stub program
can be created by linking to the appropriate stub files provided with
GDB, which implement the target side of the communication
protocol. Alternatively, gdbserver can be used to remotely debug
the program without needing to change it in any way.
i am trying to compile this code, but if i do using:
gcc prt.c portaudio.h -o prt
but i get this error:
main.c:47: undefined reference to `Pa_OpenDefaultStream'
main.c:62: undefined reference to `Pa_StartStream'
main.c:65: undefined reference to `Pa_Sleep'
main.c:66: undefined reference to `Pa_StopStream'
main.c:69: undefined reference to `Pa_CloseStream'
main.c:72: undefined reference to `Pa_Terminate'
main.c:78: undefined reference to `Pa_Terminate'
i don't know why, then i though it might be beacuse i don't have a rule (make file)
so i made one:
main: main.o
gcc main.o -o main
main.o: main.c portaudio.h
gcc -c main.c
but when i try to run it through cygwin: using "Make"
i get this message:
"make: *** No targets specified and no makefile found. Stop.
I don't understand the problem, please help me is something wrong with my makefile or is there something else wrong.
also this is the code:
main.c
#include <stdio.h>
#include "portaudio.h"
#define SAMPLE_RATE (44100)
typedef struct
{
float left_phase;
float right_phase;
}
paTestData;
static int patestCallback( const void *inputBuffer, void *outputBuffer,
unsigned long framesPerBuffer,
const PaStreamCallbackTimeInfo* timeInfo,
PaStreamCallbackFlags statusFlags,
void *userData )
{
/* Cast data passed through stream to our structure. */
paTestData *data = (paTestData*)userData;
float *out = (float*)outputBuffer;
unsigned int i;
(void) inputBuffer; /* Prevent unused variable warning. */
for( i=0; i<framesPerBuffer; i++ )
{
*out++ = data->left_phase; /* left */
*out++ = data->right_phase; /* right */
/* Generate simple sawtooth phaser that ranges between -1.0 and 1.0. */
data->left_phase += 0.01f;
/* When signal reaches top, drop back down. */
if( data->left_phase >= 1.0f ) data->left_phase -= 2.0f;
/* higher pitch so we can distinguish left and right. */
data->right_phase += 0.03f;
if( data->right_phase >= 1.0f ) data->right_phase -= 2.0f;
}
return 0;
}
static paTestData data;
int main (void) {
PaStream *stream;
PaError err;
err = Pa_OpenDefaultStream( &stream,
0, /* no input channels */
2, /* stereo output */
paFloat32, /* 32 bit floating point output */
SAMPLE_RATE,
256, /* frames per buffer, i.e. the number
of sample frames that PortAudio will
request from the callback. Many apps
may want to use
paFramesPerBufferUnspecified, which
tells PortAudio to pick the best,
possibly changing, buffer size.*/
patestCallback, /* this is your callback function */
&data ); /*This is a pointer that will be passed to
your callback*/
err = Pa_StartStream( stream );
if( err != paNoError ) goto error;
Pa_Sleep(9*1000);
err = Pa_StopStream( stream );
if( err != paNoError ) goto error;
err = Pa_CloseStream( stream );
if( err != paNoError ) goto error;
err = Pa_Terminate( );
if( err != paNoError ) goto error;
printf("Test finished.\n");
return err;
error:
Pa_Terminate();
return err;
}
and the header file portaudio.h: Portaudio.h
if you want cleaner view of main.c: main.c
I am not so sure why these messages/errors/warning are coming, please help.
also this is my folder view:
You seem to be using functions from a library for the 'Port Audio' facility, but your link line does not tell the C compiler how to find that library - so the functions show up as undefined references.
Your link line should look something like:
gcc -o main main.o -lpa
That should be macroized, but the gist is correct.
This assumes the library is in 'libpa.a' or thereabouts. If it is in 'libportaudio.so', then use -lportaudio instead of -lpa.
Using macros in the makefile:
PROGRAM = main
SOURCE = main.c
OBJECT = $(SOURCE:.c=.o)
LIBDIR = /cygdrive/c/installdir/portaudio/lib
LIBRARY = $(LIBDIR)/portaudio_x86.lib
$(PROGRAM): $(OBJECT)
$(CC) $(CFLAGS) -o $# $(OBJECT) $(LDFLAGS) $(LIBRARY)
main.o: main.c portaudio.h
You should not need an explicit compilation command for main.o; make should be able to deduce that from its internal rules. Note that the character before $(CC) must be a TAB and not spaces.
The make command only looks for a file called makefile or Makefile, to use make with a differently named makefile, you need to do make -f otherfile target.
Rename your file Make file to Makefile to have make look at its contents. Also, verify that you use one tab character (no spaces) in all of the commands under a target. You might have done that, but your cut-and-paste of the contents in this posting doesn't let us know if that is really how it is.
It would also appear that you need the PortAudio library to link to or those functions will not be defined. That is, unless they're defined in the header (I haven't used that library before...)
Did portaudio come with a .lib or anything? The header file only contains the name of the functions, not the definitions. You'll need to link against the library to get the functionality for all of those functions
Your initial problem ("Undefined reference to...") is a message from the linker saying it cannot find a definition of the functions mentioned. This means you need to add a linker argument saying that you want to add the library providing these functions (lib portaudio?) to your program. GCC's command line parameter to do so is "-l"
It seems like you need to include the library (with a -l[library name] option.
A search of portaudio compile commands shows libportaudio.a included in the gcc options.
You are probably not linking to those libraries libs (.so or .a) look at the documentation and see what libs you need to link your program with.
The other thing is that when you run "make -f Makefile" you need to have a tab in your makefile before the "gcc..." lines i.e. the command lines.
I also need to add -lm, otherwise it throws an error.
So gcc -o test test.c -lm -lportaudio