How to use fprintf?

[Anas_Deshmukh]

hello everyone,

i am calling c function from qt in which i need to use fprintf syntax but unable to do so.
i am very thankful if you provide me correct way or other alternative.

my sample code :

int empId1 // some integer
pun // file pointer
read_buff[i] // char array holding value as 0xAA, 0x2D, 0xFF . . .

my aim is to write data into .txt file from read_buff[], but unable to use fprintf my code generate blank file.
after writing txt file should content like 0xAA, 0x2D, 0xFF . . .

for(i=10;i<50;i++)
{
fprintf(pun,"%d~0x%02X,",empId1,read_buf[i]);
}

[JohanSolo]

Your problem is not related to Qt...
Did you check the file was correctly opened? Did you close the file correctly?

How did you declare your read_buff array? (Basically what its type?). COuld you try to implement a complete and simple program (whitout Qt) which reproduces the same behaviour?

[Anas_Deshmukh]

@JohanSolo thanks for your prompt reply.
below part of code works fine with c application, i need to do same thing using Qt .

is there any alternative doin same thing using qt,

int empId1=1001 
FILE *pun=NULL;
char read_buf[50];
char filename[100]={0};
sprintf(filename,"/usr/test/database/fp/%d.txt",empId1);
pun=fopen(filename,"a+");
		if(!pun)
		{
			printf("Couldnt open a file.\n");
            return -1;
		}
		else
		{
                 for(i=10;i<50;i++){
                 fprintf(pun,"%d~0x%02X,",empId1,read_buf[i]); // this line works in qt only if i add empId1 or any other string
		  //fprintf(pun,"%d,",read_buf[i]); // this line work in normal c code
			}
		}
    }

[mrjj]

hi
do you call fclose(pun) ?

[JohanSolo]

@Anas_Deshmukh said:

fprintf(pun,"%d~0x%02X,",empId1,read_buf[i]); // this line works in qt only if i add empId1 or any other string

What do mean by "only if I add empId1" ?

Edit:
Why do you add the extra "%d~" if you only want something like 0xAA,0x0B,... in your file?

[Anas_Deshmukh]

hi there,

try1 ::
fprintf(pun,"%d,",read_buf[i]) // this line wont work and i need alternative for this but this wont work with Qt

try2 ::
// after trial and err below work with Qt.
// no use of adding extra %d and empId1. but it wont work with trial 1

fprintf(pun,"%d~0x%02X,",empId1,read_buf[i]);

to avoide confusion just let me know any alternative in Qt which work exactly same as fprintf()?

[Anas_Deshmukh]

fprintf(pun,"%d,",read_buf[i])

like above fprintf() is any same API or function in qt so that i write my data into the text file...when i used above fprintf() in qt the text file is created but data was not written into the file....it was create only blank file....

[JohanSolo]

Your first trial should have difficulties to compile, or should at least crash when running, the char and int sizes are different: your read_buff is char*, i.e. each element is 1 byte, whilst the "%d" expects an object of at least 4 bytes.

Did you check that the compiler is not giving any warnings? Many problems can be solved by looking at the compiler output...

[kshegunov]

@JohanSolo

Your first trial should have difficulties to compile, or should at least crash when running, the char and int sizes are different: your read_buff is char*, i.e. each element is 1 byte, whilst the "%d" expects an object of at least 4 bytes.

While I agree in principle, most compilers don't care. This is C with variadic function(s) which basically means you can forget type-safety. What's happening is that fprintf if just reading memory it doesn't own (which most compilers will allow freely, i.e. it won't crash).

@Anas_Deshmukh

int empId1; // some integer
FILE * pun; // file pointer
char read_buff[] = { 0xAA, 0x2D, 0xFF }; // char array holding value as 0xAA, 0x2D, 0xFF . . .
int read_buff_size = 3; //< Size of the above buffer (in elements)

You can do it like this:

QFile file;
if (!file.open(pun, QFile::WriteOnly))  {
    // Can't open, error handle accordingly.
}

QTextStream out(&file);

out << empId1;
for (qint32 i = 0; i < read_buff_size; i++)
    out << "~0x" << QString::number(read_buff[i], 16);
out << endl;

file.close();

// Do not forget to close the FILE *

Kind regards.