Recently, when while coding in C language, I came across and unexpected line of code in the sprintf format argument of “/tmp/%s-XXXXXX”. Here is the snippet of the code which I got:
sprintf(tempName, "/tmp/%s-XXXXXX", filename.c_str())I would like to share the steps that helped me understand What does the XXXXXX in an sprintf format argument of “/tmp/%s-XXXXXX”.
Why ‘XXXXXX in an sprintf format argument of “/tmp/%s-XXXXXX’ is seen ?
This error is seen because this sprintf call is probably composing a template for use with mktemp(), mkstemp(), mkdtemp() or a similar function. The above given POSIX functions are declared in <unistd.h>:
The Xs do not have any particular meaning for sprintf, but are interpreted by the next function called with tempName.
A simple and optimal solution is to limit the number of characters from filename.c_str() to make sure all Xs are present at the end.
A detailed solution to undestand to fix the ‘XXXXXX in an sprintf format argument of “/tmp/%s-XXXXXX’ is provided below:
How to undestand the ‘XXXXXX in an sprintf format argument of “/tmp/%s-XXXXXX”?
To understand ‘XXXXXX in an sprintf format argument of “/tmp/%s-XXXXXX”‘; you will have to follow the below-mentioned steps to fix the error:
The sprintf call is mostly making a template to use with mktemp(), mkstemp(), mkdtemp() or a similar function. The Xs do not have any particular meaning for sprintf, but are interpreted by the next function called with tempName.The above given POSIX functions are declared in <unistd.h>.
Here I would like to show you a brief overview of the functions to understand the problem:
The mktemp() method takes a file name template and changes a portion of it to create a new name for the file.
The file name is not assured to be present at the time of the function being called and is compatible for the use by your application.
The given template is possible with any file name with some number of Xs appended to it, a simple example for this /tmp/temp.XXXXXX. The trailing Xs is to be replaced with a unique alphanumeric combination.
The number of unique file names mktemp() will be able to return depending on the number of Xs provided; six Xs will result in mktemp() selecting one of 56800235584 (626) possible temporary file names.
A fix is to limit the number of characters from filename.c_str() to make sure all Xs are present at the end as present in the code given below:
char tempname[32];
snprintf(tempName, sizeof tempName, "/tmp/%.19s-XXXXXX", filename.c_str());This should help you understand ‘XXXXXX in an sprintf format argument of “/tmp/%s-XXXXXX’.
Conclusion
To fix ‘XXXXXX in an sprintf format argument of “/tmp/%s-XXXXXX” is to limit the number of characters from filename.c_str() to make sure all Xs are present at the end.