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Asked: 2026-06-18T22:40:17+00:00

According to http://linux.die.net/man/3/sprintf and http://www.cplusplus.com/reference/cstdio/sprintf/ sprintf() and family return the number of characters written

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According to http://linux.die.net/man/3/sprintf and http://www.cplusplus.com/reference/cstdio/sprintf/ sprintf() and family return the number of characters written on success. On failure, a negative value is returned. I would assume that an error could occur if the format string is malformed so a negative return value could indicate something other than a malloc() error. Does errno get set to indicate what the error was?

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  1. Editorial Team

    C++ defers to C and C does not require or mention errno in the description of sprintf() and family (although for certain format specifiers, these functions are defined to call mbrtowc(), which may set EILSEQ in errno)

    POSIX requires that errno is set:

    If an output error was encountered, these functions shall return a negative value and set errno to indicate the error.

    EILSEQ, EINVAL, EBADF, ENOMEM, EOVERFLOW are mentioned explicitly: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html

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