I am trying to compile this program https://gist.github.com/jrabbit/1042021
I am using this https://doc.opensuse.org/projects/satsolver/11.2/sha1_8h_source.html sha1.h file. However if I try to compile the program gcc gives me the following error (gcc on windows)
c:/mingw/bin/../lib/gcc/mingw32/6.3.0/../../../libmingw32.a(main.o):(.text.start
up+0xa0): undefined reference to `WinMain#16'
collect2.exe: error: ld returned 1 exit status
gcc did not recognise type u_int32_t so I changed them to unit32_t in sha1.c code
What could be wrong there?
The library doesn't have main function. Any C program must have a main function to compile.
So either you create a main.c file and include the library in it.
Or in line 251 of sha1.c change #if 0 to #if 1 which will open the template main function included in the library.
Note that the template 'main` function has some bugs. Replace it with something like that:
#define BUFSIZE 10
int
main(int argc, char **argv)
{
SHA1_CTX ctx;
unsigned char hash[20], buf[BUFSIZE];
int i;
for(i=0;i<BUFSIZE;i++)
{
buf[i] = i + '0';
printf("%i", i);
}
printf("\n");
SHA1Init(&ctx);
for(i=0;i<BUFSIZE;i++)
SHA1Update(&ctx, buf + i, 1);
SHA1Final(hash, &ctx);
printf("SHA1=");
for(i=0;i<20;i++)
printf("%02x", hash[i]);
printf("\n");
return 0;
}
Related
I only used C 2-3 times. Following hello world tutorial did not help. the function should just print to std out console.
#include <stdio.h>
void my_putstr(char* param_1) {
char *t ;
for (t = param_1; *t != '\0'; t++) {
printf("%s", t);
}
}
int main(){
my_putstr("abc");
return 0;
}
How to run this program? I do have main to call & test my putstr function.
I do this:
gcc file.c -o file
gcc file
But it still gives me the error of "main":
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status
I do have the main function. What's wrong?
gcc file.c -o file
gcc file
That second line will try to compile the executable file that you created with the first line and, since it's not C source(a), that won't end too well :-)
You need to run the file with something like:
./file
And, just as an aside, you should strive to make your programs more readable, such as with:
#include <stdio.h>
// my_putstr:
// Output the given string multiple times, each time starting
// at the next character. So, for "1234", it would output
// "1234 234 34 4" (without the spaces).
void my_putstr(char *str) {
// Start at position 0, 1, m2, etc until no more string left.
for (char *ptr = str; *ptr != '\0'; ptr++) {
printf("%s", ptr);
}
}
int main(void) {
my_putstr("abc");
return 0;
}
Changes made:
Comments are quite handy if you ever come back to the code after some time;
You should try to avoid simple variable names, use names that make the intent clear (about the only exception are simple i, j, k loop variables;
The two canonical forms of main are int main(int argc, char **argv) (though the "or equivalent" phrase in the standard also allows for int main(int argc, char *argv[])) or int main(void), you should try to stick with them.
By the way, the description in the comments above is an accurate representation of the way the code works. If, instead, you just want to output a string (i.e., not the 1234 234 34 4 behaviour), you're probably better off with something like:
void my_putstr(char *str) {
// Output each character, one at a time.
for (char *ptr = str; *ptr != '\0'; ptr++)
putchar(*ptr);
// Output newline (if desired).
putchar('\n');
}
(a) The gcc program is quite capable of taking other input file types (like object files, assembler files, and so on) but I'm not sure finished executables are one of those types.
This is my main file
#include<stdio.h>
#include<string.h>
#include "ssv.c"
int main() {
int i,length,acct;
float amnt;
char data[1000], record[1000];
FILE *x = fopen("students.ssv","rt");
while(!feof(x)) {
for (i = 0; data[i] != '\n'; i++) {
record[i] = data[i];
length = i + 1;
}
record[length] = '\0';
parse(record,&acct,&amnt);
fgets(data,999,x);
}
fclose(x);
return 0;
}
This is my ssv.c file
#include<stdio.h>
void parse(char record[], int *acct, float *amnt){
sscanf(record,"%d %f",acct,amnt);
}
For some reason, these two programs are not working very well together. I am still getting used to modular programming. I keep getting the messages "undefined reference to main" and "multiple definition of".
My main goal here is to parse a file like
100 -10.5
13 -2.4
into corresponding fields. Please advise!
The first iteration of the while loop uses data before it has read the line. It should be:
while(fgets(data, sizeof data, x)) {
parse(data,&acct,&amnt);
}
You don't need to subtract 1 from the size of data when calling fgets().
There's no reason to copy data to record. You can simply parse data (the parse() function will ignore the newline). fgets() ends the string with a null terminator, you don't need to add it yourself.
#include should only be used for .h files, not .c files. You combine object files using the linker. So get rid of #include "ssv.c", replace it with #include "ssv.h". This file should just contain a declaration of parse().
void parse(char record[], int *acct, float *amnt);
Compile the two programs using:
gcc main.c ssv.c
Or you can compile each file separately then link them:
gcc -c main.c
gcc -c ssv.c
gcc main.o ssv.o
I'm writing an application using libao for audio output. The portion
of my program that calls into libao lives in a shared object:
// playao.c
// compile with: gcc -shared -o libplayao.so playao.c -lao -lm
#include <ao/ao.h>
#include <stdio.h>
#include <math.h>
void playao(void) {
int i;
unsigned char samps[8000];
ao_initialize();
ao_sample_format sf;
sf.bits = 8;
sf.rate = 8000;
sf.channels = 1;
sf.byte_format = AO_FMT_NATIVE;
sf.matrix = "M";
ao_device *device = ao_open_live(ao_default_driver_id(), &sf, NULL);
if(!device) {
puts("ao_open_live error");
ao_shutdown();
return;
}
for(i = 0; i < 8000; ++i) {
float time = (float)i / 8000;
float freq = 440;
float angle = time * freq * M_PI * 2;
float value = sinf(angle);
samps[i] = (unsigned char)(value * 127 + 127);
}
if(!ao_play(device, (char *)samps, 8000)) {
puts("ao_play error");
}
ao_close(device);
ao_shutdown();
}
If I link against this shared object in a program, it works fine:
// directlink.c
// compile with: gcc -o directlink directlink.c libplayao.so -Wl,-rpath,'$ORIGIN'
void playao(void);
int main(int argc, char **argv) {
playao();
return 0;
}
However, if I use dlopen/dlsym to invoke it, there are no errors, but the
program does not cause any sound to be emitted:
// usedl.c
// compile with: gcc -o usedl usedl.c -ldl
#include <dlfcn.h>
#include <stdio.h>
int main(int argc, char **argv) {
void *handle = dlopen("./libplayao.so", RTLD_LAZY);
if(!handle) {
puts("dlopen failed");
return 1;
}
void *playao = dlsym(handle, "playao");
if(!playao) {
puts("dlsym failed");
dlclose(handle);
return 1;
}
((void (*)(void))playao)();
dlclose(handle);
return 0;
}
However, running usedl with LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libao.so.4
does work. So there's something about libao that wants to be loaded when the
program starts up, and doesn't like being loaded any later.
Why is this? Is there any way to work around this, so that libao works
correctly even if loaded later in the program's execution?
I'm running Debian 10 "buster" if it matters.
I asked about this on the #xiph channel on Freenode and xiphmont suggested turning turning on verbose mode. Once I did that, the failing case started getting the message:
ERROR: Failed to load plugin /usr/lib/x86_64-linux-gnu/ao/plugins-4/libalsa.so => dlopen() failed
So libao itself is trying to dlopen something, and it's failing. It's not showing me any more details, so I ran the program under GDB and set a breakpoint on dlopen. After hitting the dlopen breakpoint for libalsa and running finish, I tried finding what the error was by using print (const char *)dlerror(). And with this, I get a more detailed error:
/usr/lib/x86_64-linux-gnu/ao/plugins-4/libalsa.so: undefined symbol: ao_is_big_endian
So ao's libalsa plugin is trying to reference symbols back in libao, but it's not finding them. Why could this be? Referencing the dlopen documentation, I see:
Zero or more of the following values may also be ORed in flags:
RTLD_GLOBAL: The symbols defined by this shared object will be made available for symbol resolution of subsequently loaded shared objects.
RTLD_LOCAL: This is the converse of RTLD_GLOBAL, and the default if neither flag is specified. Symbols defined in this shared object are not made available to resolve references in subsequently loaded shared objects.
Because my dlopen call only used RTLD_LAZY and didn't include RTLD_GLOBAL or RTLD_LOCAL, it defaulted to RTLD_LOCAL, which does not expose the symbols in the shared object (like ao_is_big_endian) to subsequently loaded shared objects (like libalsa.so).
So, I tried changing the code from:
void *handle = dlopen("./libplayao.so", RTLD_LAZY);
To:
void *handle = dlopen("./libplayao.so", RTLD_LAZY | RTLD_GLOBAL);
And lo and behold, it works!
I created a program in C and I tried to compile it. When I use my gcc 4.8.1 compiler in Widows everything worked and my program too.
I compiled with the following arguments:
gcc -std=c99 -O2 -DCONTEST -s -static -lm children.c
But in linux I getting the following error:
/usr/lib/gcc/i486-linux-gnu/4.7/../../../i386-linux-gnu/crt1.o: In function `_start':
(.text+0x18): undefined reference to `main'
collect2: error: ld returned 1 exit status
Why is that? My programm is working and I can't understand why I getting compiling errors in linux.
My code is:
/*---------------------*/
/* included files */
/*---------------------*/
#include <stdio.h>
#include <stdlib.h>
/*---------------------*/
/* defined constants */
/* for restriction */
/*---------------------*/
#define MIN 1
#define MAX 1000000
#define IOERROR 5 // 'Input/Output Error'
/*---------------------*/
/* function prototypes */
/*---------------------*/
int main();
FILE *read_input(const char *filename_r);
int count_children(FILE *input);
int pass_heights(FILE *input, int *children, int size);
int check_tall(const int *children, int size);
void write_output(const int total,const char *filename_w);
/*---------------------*/
/* start of program */
/*---------------------*/
int main() {
const char *filename_r = "xxx.in";
const char *filename_w = "xxx.out";
FILE *input = read_input(filename_r);
int size = count_children(input);
int *children = malloc(size * sizeof *children);
if (children==NULL)
exit(1); //General application error
pass_heights(input, children, size);
fclose(input);
int total = check_tall(children, size);
free(children);
write_output(total,filename_w);
return 0;
}
FILE *read_input(const char *filename_r) {
FILE *input = fopen(filename_r, "r");
if(input == NULL)
exit(IOERROR);
return input;
}
int count_children(FILE *input) {
int count = 0;
fscanf(input, "%d",&count);
if(count > MAX || count < MIN)
exit(1); //General application error
return count;
}
int pass_heights(FILE *input, int *children, int size) {
for(int i = 0; i < size; i++)
fscanf(input, "%d",&children[i]);
return *children;
}
int check_tall(const int *children, int size) {
int total = 0;
int tmp_max = 0;
for(int i = size - 1; i >= 0; i--)
{
if(children[i] > tmp_max) {
tmp_max = children[i];
total++;
}
}
return total;
}
void write_output(const int total,const char *filename_w) {
FILE *output = fopen(filename_w, "w");
if(output == NULL)
exit(IOERROR);
fprintf(output, "%d\n", total);
fclose(output);
}
You used -static option, which modifies the way executable is linked.
I was unable to reproduce your exact error message, but on my Linux it says that it is unable to link with -lc in static mode, and under my OSX it says that it is unable to locate -lcrt0.o. For me in both case, this means that the system is unable to locate the static stub.
If you remove -static it should work. If not, your problem is very strange.
The error you show indicates the linker is not finding the main() function in your code. As it is evident that you have included it in the source file, it is also evident you are not compiling with that command line (or you are compiling in other directory where you have a non-main() source called children.c, perhaps the build system makes a touch children.c if it doesn't find the source, and then compiles it --on that case it will not have a main() routine). Check that the files are properly created and where, as I think you aren't compiling that file anyway.
Try to use simple options before you go to more complicated ones. Try something like:
gcc -std=c99 -o children children.c
before trying to experiment with optimization or static linking anyway. Also, dynamic linking is normally better than static, so you'll get smaller executables (8Kb vs. 800Kb, and multiple copies of libc loaded per executable). Also, you don't need to include -lm as you aren't using any of the <math.h> functions (having it doesn't hurt anyway).
I have compiled your source with the following command line without any problem, but I do have support for statically linked executables and perhaps you don't (the command line I have put above would work in any linux, I suppose)
$ make CC='gcc' CFLAGS='-std=c99 -O2 -DCONTEST' LDFLAGS='-s -static -lm' children
gcc -std=c99 -O2 -DCONTEST -s -static -lm children.c -o children
children.c: In function ‘pass_heights’:
children.c:81:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result]
children.c: In function ‘count_children’:
children.c:69:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result]
I have this c program:
#include <sys/types.h>
#include "ourhdr.h"
int glob = 6; /* external variable in initialized data */
char buf[] = "a write to stdout\n";
int
main(void)
{
int var; /* automatic variable on the stack */
pid_t pid;
var = 88;
if (write(STDOUT_FILENO, buf, sizeof(buf)-1) != sizeof(buf)-1)
err_sys("write error");
printf("before fork\n"); /* we don't flush stdout */
if ( (pid = fork()) < 0)
err_sys("fork error");
else if (pid == 0) { /* child */
glob++; /* modify variables */
var++;
} else
sleep(2); /* parent */
printf("pid = %d, glob = %d, var = %d\n", getpid(), glob, var);
exit(0);
}
In the header file "ourhdr.h" (located in the same folder) i defined several functions, such as err_sys().
I get this error while compiling with gcc:
In function "main":
undefined reference to "err_sys"
How can i get this working? I can post the header file here if needed. Thank you.
** EDIT: ** This is the ourhdr.h file: http://pastebin.com/fMUiG4zU
You have included the header file with the declaration of err_sys. Ensure you have also an implementation that is passed to the linker. Background:
The compiler compiles a module to an object file:
g++ -c modul1.c generates modul1.o
g++ -c modul2.c generates modul2.o
Each of the modules can reference functions that are defined in a included header file. Up to here, no actual implementation of that function is needed.
In the next step, the linker links toghether all object files (and libraries):
g++ modul1.o modul2.o generates ./a.out or similar
In the second step, an implementation for all used functions is needed. Be sure you provided it!
(P.S.: Some compilers allow compiling and linking with one command, if you have multiple modules you can perhaps add them to a single gcc-call. I'd recomment to use make though)
I think what's likely to happen is that you have a header, ourhdr.h, containing the definition of the function, but the implementation is in a different file: ourhdr.c. In that case, if you try to compile without including ourhdr.c you'll get a reference error:
$ gcc main.c
/bin/ld: /tmp/ccVzNF6w.o: in function `main':
main.c:(.text+0x38): undefined reference to `err_sys'
To fix it, you need to compile like this:
$ gcc main.c ourhdr.c
Another option is to define the body of the function in ourhdr.h:
// ourhdr.h
#include <stdio.h>
void err_sys(const char* str);
void err_sys(const char* str) {
fprintf(stderr, "%s\n", str);
}
In that case, gcc main.c should work.
For me, it is compiling and working fine if you write the function name is written correctly.