I'm having some trouble to append a structure to a file:
OS: Ubuntu 14.04
Struct:
struct baris
{
char name[30];
char trusted[1];
int phone;
int id;
};
Func:
addNewBariga()
{
char answer[30];
struct baris new;
while(1){
printf("Enter new Barigas' ID please.");
scanf("%d",&new.id);
printf("Enter new Barigas' name please.\n");
scanf("%s",new.name);
printf("Enter new Barigas phone please. \n");
scanf("%d", &new.phone);
printf("Is Bariga trusted?\n\t[Y/N]:");
scanf("%s",new.trusted);
while(1)
{
if(strcmp(new.trusted,"Y") != 0 && strcmp(new.trusted,"y") != 0)
{
printf("%s",new.trusted);
printf("\nWrong command givven.\t\n[Y/N]:");
scanf("%s",&new.trusted);
}
else
break;
}
printf("Values you've entered:\n\tID:%d\n\tName: %s\n\tPhone: %d\n\tTrustworth:%s\nWould you like to proceed to saving?\n[Y/N]:\n",new.id,new.name,new.phone,new.trusted);
scanf("%s",&answer);
if(strcmp(answer,"Y") ==0 || strcmp(answer,"y")==0) //Process to saving
{
printf("saving...");
confPtr = fopen(filePath , "ab");
//fwrite(new.id, sizeof(new.id), 1, confPtr);
fwrite(&new, sizeof(struct baris), 1, confPtr);
fclose(confPtr);
break;
}
}
What I'm getting:
fabio\00\00\00\00\00\00\00\00\00fab\00\00\00\00\00\00\00\00\00fab\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00 <1\B5y\00\00\00\00\00\00\00fab\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00\00 \C5f\DAy\00\00\00\00\00\00\00
That output looks basically correct, what did you expect?
You're writing binary data to a binary file. Binary files are not very easy to inspect manually.
The first member of the structure, name, will always be 30 bytes long in the output for example.
Note as pointed out by #BLUEPIXY in a comment that this:
scanf("%s",new.trusted);
triggers undefined behavior if a non-zero length is entered, since trusted is only 1 character long that is consumed by the string terminator. You should increase its length, or (much better!) stop using direct scanf() like this and instead read a whole line of input with fgets() and parse it using sscanf().
Also, when using functions that can fail (like scanf(), sscanf() or fgets()) you must check the return values before relying on them to have succeeded.
Related
I wrote a small program in C that creates a list of students in a binary file. I call function fsearch() (below) to search for a specified student and change his data, but the data seems not to be modified.
// the file is opened in mode "wb+"
int fsearch(FILE *f)
{
student s;
float matsearch;
printf("enter the matricule you want to find ");
scanf("%f",&matsearch);
rewind(f); // starting the search from the beginning
while(fread(&s,sizeof(student),1,f)==1 && s.mat!=matsearch);
if(s.mat==matsearch)
{
printf("we found what searched for\n");
printf("name: %s\n",s.fname);
printf("last name: %s\n",s.lname);
printf("matricule: %.f\n",s.mat);
fseek(f,-sizeof(student),SEEK_CUR);
student a;
scanf("%s",&(a.fname));
scanf("%s",&(a.lname));
scanf("%d",&(a.mat));
if(fwrite(&a,sizeof(student),1,f)==1)
{
printf("successfully wrote"); // this message does get printed
}
return(1); // successfully found
}
printf("we didn't find what you searched for\n");
return(0);
}
In addition to the one posted by bluesawdust, I found some other mistakes in the code:
// the file is opened in mode "wb+": this means that your file was destroyed on open (see here). You might want to use "rb+"
since you didn't initialize your student s structure (and no record was ever written in it because of my previous point) s.mat contains a random value
scanf("%d",&(a.mat));: as for printf, you should change the format string to "%f" (but actually you should use a string type, comparing floats with == is not good practice because of the roundings)
sizeof(student) is unsigned, so negating it is not appropriate here. You should cast it to an int before negating.
int main(void){
FILE *ifp; //input file pointer
int totalClock; //total clock count
// BEGIN OPERATIONS=============================
ifp=fopen("prog1.asy.txt", "r");
system("PAUSE");
assert(ifp!=NULL);
//populate the instMem with inst===================
int i=0;
//system("PAUSE");
for (i=0;i<512;i++)
{
inst temp=parser(ifp);
if (temp.opcode==-1)
break;
instMem[i]=temp;
printf("%s\n", instMem[i].rawCode);
}
printf("\n%d instructions parsed\n", i-1);
system("PAUSE");// PAUSE TO CHECK CODE PARSING IS CORRECT========
int cont=0;
while (cont==0){
//begin sim================================================
//initialize the mem=======================================
int i;
for (i=0;i<512;i++)
data[i]=0;
for (i=0;i<32;i++)
reg[i]=0;
IF_Time=0;
ID_Time=0;
EX_Time=0;
MEM_Time=0;
WB_Time=0;
//prompt input parameters===================================
printf("Memory access time: c=");
scanf("%d", &c);
printf("\nMultiply time: m=");
scanf("%d", &m);
printf("\nExecute time: n=");
scanf("%d", &n);
assert(c>0);
assert(m>0);
assert(n>0);
//start execution now that the program has been broken to unparsed strings====
while (0==0)
{
WB();
MEM();
if (MEM_WB.instruction.opcode==HALT)
break;
EX();
ID();
IF();
totalClock++;
system("PAUSE");
}
//PRINT RESULTS=============================================
printf("Run again with new parameters? 0=yes");
scanf("%d", &cont);
}
fclose(ifp);
system("PAUSE");
return 0;
}
struct inst parser(FILE *ifp){
char str[100];
struct inst temp;
if (fgets(str, 100, ifp)==NULL) {
inst temp={"NULL", -1,0,0,0};
}
else {
inst temp={str, 0,0,0,0};
puts(str);
}
return temp;
}
I am trying to read in a test file so that i can parse it into strings for analysis later. It opens the test file but it doesn't read the lines of test in the code. Is there something I am doing wrong.
Your parser functions only reads once from the file and does nothing with the result (since temp would be a local variable to the if branch, not to the function). First thing is to remove inst from inst temp = ... to see that it reads the first instruction. Then, you need to make that function loop over all lines in the file.
First of all, you need to format your source code on this page to make it more readable.
For parser(), I don't think you can return a structure. So please use a pointer instead. And, as Mihai mentions, "temp" is a temporary variable located on the stack, and it will be destroyed when returning from function parser().
I don't see the declarations of variables in the code snippet:
IF_Time=0;
ID_Time=0;
EX_Time=0;
MEM_Time=0;
WB_Time=0;
So I assume you could remove some unused code to make the question clear.
The last thing is: to analyze log files, shell scripts is more suitable than C. If you're not working on a UNIX/Linux box, you could also use Perl/Python if you want. They are all less error prone and easy to debug when used to analyze log files.
I have an array of structs and they get saved into a file. Currently there are two lines in the file:
a a 1
b b 2
I am trying to read in the file and have the data saved to the struct:
typedef struct book{
char number[11];//10 numbers
char first[21]; //20 char first/last name
char last[21];
} info;
info info1[500]
into num = 0;
pRead = fopen("phone_book.dat", "r");
if ( pRead == NULL ){
printf("\nFile cannot be opened\n");
}
else{
while ( !feof(pRead) ) {
fscanf(pRead, "%s%s%s", info1[num].first, info1[num].last, info1[num].number);
printf{"%s%s%s",info1[num].first, info1[num].last, info1[num].number); //this prints statement works fine
num++;
}
}
//if I add a print statement after all that I get windows directory and junk code.
This makes me think that the items are not being saved into the struct. Any help would be great. Thanks!
EDIT: Okay so it does save it fine but when I pass it to my function it gives me garbage code.
When I call it:
sho(num, book);
My show function:
void sho (int nume, info* info2){
printf("\n\n\nfirst after passed= %s\n\n\n", info2[0].first); //i put 0 to see the first entry
}
I think you meant int num = 0;, instead of into.
printf{... is a syntax error, printf(... instead.
Check the result of fscanf, if it isn't 3 it hasn't read all 3 strings.
Don't use (f)scanf to read strings, at least not without specifying the maximum length:
fscanf(pRead, "%10s%20s%20s", ...);
But, better yet, use fgets instead:
fgets(info1[num].first, sizeof info1[num].first, pRead);
fgets(info1[num].last, sizeof info1[num].last, pRead);
fgets(info1[num].number, sizeof info1[num].number, pRead);
(and check the result of fgets, of course)
Make sure num doesn't go higher than 499, or you'll overflow info:
while(num < 500 && !feof(pRead)){.
1.-For better error handling, recommend using fgets(), using widths in your sscanf(), validating sscanf() results.
2.-OP usage of feof(pRead) is easy to misuse - suggest fgets().
char buffer[sizeof(info)*2];
while ((n < 500) && (fgets(buffer, sizeof buffer, pRead) != NULL)) {
char sentinel; // look for extra trailing non-whitespace.
if (sscanf(buffer, "%20s%20s%10s %c", info1[num].first,
info1[num].last, info1[num].number, &sentinel) != 3) {
// Handle_Error
printf("Error <%s>\n",buffer);
continue;
}
printf("%s %s %s\n", info1[num].first, info1[num].last, info1[num].number);
num++;
}
BTW: using %s does not work well should a space exists within a first name or within a last name.
I'm completely new to C and I'm working on a program which has to read in 3 lines from a text file(two numbers and a mathematical symbol) and write out the result. So for example:
The text file looks like:
1
4
*
and my program should be able to read the 3 lines and write out something like "1*4 = 4" or something.
I managed to get to a point where i can read the 3 lines in and show them on screen, so I thought I should put the two numbers in one array and the symbol in another one. The problem is, that I tried to see if the arrays contain the numbers I put in them and my output has some huge numbers in it and I'm not sure why.
Here's the code i wrote:
#include <stdio.h>
#include <io.h>
#include <string.h>
int main(void)
{
int res = 1; /*Creates an integer to hold the result of the check for the file*/
const char *file = "input.txt"; /*String holding the name of the file with the input data*/
res = access(file,R_OK); /*Checks if the file "input.txt" exists*/
if(res == -1)
{ /*IF the file doesn't exist:*/
FILE *input = fopen("input.txt","w"); /*This creates a file called "input.txt" in the directory of the program*/
char write[] = "1\n1\n+"; /*This variable holds the string that's to be written to the file*/
fprintf(input,"%s",write); /*This writes the variable "write" to the file*/
printf("input.txt file created!"); /*Tells you the file is created*/
fclose(input); /*Closes the file after it's done*/
}
else
{ /*IF the file exists:*/
FILE *f = fopen("input.txt","r");
//char line[ 5000 ];
//while ( fgets ( line, sizeof line, f ) != NULL )
//{
// fputs ( line, stdout );
//}
char line[5000];
char nums[2];
char symbol[1];
int i = 0;
while(fgets(line,sizeof line,f)!=NULL)
{
i++;
if(i < 3)
{
fputs(nums,f);
}
else
{
fputs(symbol,f);
}
printf("%d,%d",nums,symbol);
}
printf("\n\n\n");
scanf("\n");
}
return 0;
}
Any help would be greatly appreciated!
Thank you in advance
If you require any more information i will provide it.
This is a self-explanatory algorithm. Also, here is the code that does the operation you are looking for. Generally, the complex operations are accomplished using stack, push and pop method. Once the operators are pushed. One need to apply the BODMAS rule,to evaluate the expression. Since the problem given to you is simple, a simple expression evaluation. This can be simply achieved by FIFO. Here is the algorithm, general explanation. Afterwards, the code is present. This code is well tested.You can extend it to do operations like +,-,division /, %, etc. If you like my answer please appreciate.
#include "stdio.h"
int main(int argc, char *argv[])
{
FILE *fp_op;
int buff[2]; /** assuming a simple operation, thus the buffer size is 3 only, the last one is to store the NULL **/
char operat_buff[2]; /** assuming this operation we can extend it to evaluate an expression **/
fp_op = fopen("calc.txt","rb");
if ( fp_op == 0 )
{
perror("The file doesn't exist to calculate\r\n");
goto error;
}
/** Read the two numbers here **/
fscanf(fp_op,"%d",&(buff[0]));
printf("The buff[1] = %d\r\n",buff[0]);
fscanf(fp_op,"%d",&(buff[1]));
printf("The buff[1] = %d\r\n",buff[1]);
/** read the next line now \n **/
operat_buff[0] = fgetc(fp_op);
/** read the actual character now **/
operat_buff[0] = fgetc(fp_op);
printf("The operat_buff[0] = %d\r\n",operat_buff[0]);
/** Read operation completed **/
/** use switch here **/
switch(operat_buff[0])
{
case '*':
printf("The multiplication result=%d\r\n",buff[0]*buff[1]);
break;
case '+':
printf("The Addition result=%d\r\n",buff[0]+buff[1]);
break;
default:
printf("Add more operations\r\n");
}
return 0;
error:
return -1;
}
I assume that the calc.txt was something like this.
calc.txt
3
5
*
Note: This code is compiled and verified.It compiles with zero warnings. It does the error checking too. You can directly copy and paste it.
What are you reading from the files are simply characters codes: the program has no way of figuring by itself that the character "4" corresponds to the integer number 4. The %d placeholder of printf expects int variables, or it won't work.
If you want just to print the characters you have to save them in char variables (or a char array) and use the placeholder %c in printf. If you want to actually use the numbers and symbols in your program you have more work to do.
Not only in C, but I think in most languages you have to "parse" the characters to numbers.
In C you can use the functions atoi or atol (you have to #include <stdlib.h>) in order to do this conversion.
In order to parse the symbol I'm afraid you will have to use an if or a switch to read the character and perform the operation accordingly.
For example your loop could look like:
while(fgets(line,sizeof line,f)!=NULL)
{
int op1;
int op2;
int res;
char symbol;
i++;
switch (i) {
case 1:
//First line is first operand
op1 = atoi(line);
printf("op1 %d\n",op1);
break;
case 3:
//Second line is second operand
op2 = atoi(line);
printf("op2 %d\n",op2);
break;
//Fifth line is the operator, could be +,-,%./ or anything
case 5:
symbol = line[0];
printf("operand %c\n",symbol);
switch(symbol) {
case '+':
res = op1+op2;
break;
case '-':
res = op1-op2;
break;
default:
//operation not defined, return
return;
}
printf("%d%c%d = %d",op1,symbol,op2,res);
}
}
printf("%d,%d",nums,symbol);
In your code nums and symbol are strings, you can't print them with %d. What you are getting are the addresses of the nums and symbol arrays, respectively - even if that's not the right way of printing an address.
You'll likely want to convert them to integers, using strtol or sscanf and then use those to perform the computation.
I'm making a small console-based rpg, to brush up on my programming skills.
I am using structures to store character data. Things like their HP, Strength, perhaps Inventory down the road. One of the key things I need to be able to do is load and save characters. Which means reading and saving structures.
Right now I'm just saving and loading a structure with first name and last name, and attempting to read it properly.
Here is my code for creating a character:
void createCharacter()
{
char namebuf[20];
printf("First Name:");
if (NULL != fgets(namebuf, 20, stdin))
{
char *nlptr = strchr(namebuf, '\n');
if (nlptr) *nlptr = '\0';
}
strcpy(party[nMember].fname,namebuf);
printf("Last Name:");
if (NULL != fgets(namebuf, 20, stdin))
{
char *nlptr = strchr(namebuf, '\n');
if (nlptr) *nlptr = '\0';
}
strcpy(party[nMember].lname,namebuf);
/*Character created, now save */
saveCharacter(party[nMember]);
printf("\n\n");
loadCharacter();
}
And here is the saveCharacter function:
void saveCharacter(character party)
{
FILE *fp;
fp = fopen("data","a");
fwrite(&party,sizeof(party),1,fp);
fclose(fp);
}
and the loadCharacter function
void loadCharacter()
{
FILE *fp;
character tempParty[50];
int loop = 0;
int count = 1;
int read = 2;
fp= fopen("data","r");
while(read != 0)
{
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
printf("%d. %s %s\n",count,tempParty[loop].fname,tempParty[loop].lname);
loop++;
count++;
}
fclose(fp);
}
So the expected result of the program is that I input a name and last name such as 'John Doe', and it gets appended to the data file. Then it is read in, maybe something like
1. Jane Doe
2. John Doe
and the program ends.
However, my output seems to add one more blank structure to the end.
1. Jane Doe
2. John Doe
3.
I'd like to know why this is. Keep in mind I'm reading the file until fread returns a 0 to signify it's hit the EOF.
Thanks :)
Change your loop:
while( fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp) )
{
// other stuff
}
Whenever you write file reading code ask yourself this question - "what happens if I read an empty file?"
You have an algorithmic problem in your loop, change it to:
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
while(read != 0)
{
//read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
printf("%d. %s %s\n",count,tempParty[loop].fname,tempParty[loop].lname);
loop++;
count++;
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
}
There are ways to ged rid of the double fread but first get it working and make sure you understand the flow.
Here:
read=fread(&tempParty[loop],sizeof(tempParty[loop]),1,fp);
printf("%d. %s %s\n",count,tempParty[loop].fname,tempParty[loop].lname);
You are not checking whether the read was successful (the return value of fread()).
while( 1==fread(&tempParty[loop],sizeof*tempParty,1,fp) )
{
/* do anything */
}
is the correct way.
use fopen("data","rb")
instead of fopen("data","r") which is equivalent to fopen("data","rt")
You've got the answer to your immediate question but it's worth pointing out that blindly writing and reading whole structures is not a good plan.
Structure layouts can and do change depending on the compiler you use, the version of that compiler and even with the exact compiler flags used. Any change here will break your ability to read files saved with a different version.
If you have ambitions of supporting multiple platforms issues like endianness also come into play.
And then there's what happens if you add elements to your structure in later versions ...
For robustness you need to think about defining your file format independently of your code and having your save and load functions handle serialising and de-serialising to and from this format.