std::tolower

From Cppreference

C++ Standard Library
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Strings library
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Functions Character manipulation isalnum isalpha islower isupper isdigit isxdigit isblank (C++11) iscntrl isgraph isspace isprint ispunct tolower toupper Conversions to numeric formats atof atoi strtol strtoul strtof String manipulation strcpy strncpy strcat strncat strxfrm String examination strlen strcmp strncmp strcoll strchr strrchr strspn strcspn strpbrk strstr strtok Memory manipulation memchr memcmp memset memcpy memmove Miscellaneous strerror

Defined in header <cctype>
int tolower( int ch );

Converts the given character to lowercase.

[edit] Parameters

ch

-

character to be converted

[edit] Return value

lowercase version of ch or unmodified ch if no lowercase version is listed in the current C locale.

[edit] See also

toupper	converts a character to uppercase (function)
tolower(std::locale)	converts a character to lowercase using the ctype facet of a locale (function template)
towlower	converts a wide character to lowercase (function)