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number generation rand RAND_MAX remainder remainderf remainderl remquo remquof remquol rint rintf rintl round roundf roundl scalbln scalblnf scalblnl scalbn scalbnf scalbnl signbit sin sinf sinh sinhf sinhl sinl sqrt sqrtf sqrtl srand tan tanf tanh tanhf tanhl tanl tgamma tgammaf tgammal trunc truncf truncl Type-generic math _Complex_I _Imaginary_I Program support abort atexit at_quick_exit exit EXIT_FAILURE EXIT_SUCCESS getenv getenv_s jmp_buf longjmp Program support utilities quick_exit raise setjmp SIGABRT SIGFPE SIGILL SIGINT signal SIGSEGV SIGTERM sig_atomic_t SIG_DFL SIG_ERR SIG_IGN system _Exit Strings atof atoi atol atoll btowc c16rtomb c32rtomb char16_t char32_t isalnum isalpha isblank iscntrl isdigit isgraph islower isprint ispunct isspace isupper iswalnum iswalpha iswblank iswcntrl iswctype iswdigit iswgraph iswlower iswprint iswpunct iswspace iswupper iswxdigit isxdigit mblen mbrlen mbrtoc16 mbrtoc32 mbrtowc mbsinit mbsrtowcs mbsrtowcs_s mbstate_t mbstowcs mbstowcs_s mbtowc 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characters

在头文件<stdlib.h>中定义



int atoi(const char * str);



long atol(const char * str);



long long atoll(const char * str);


(自C99以来)

解释str指向的字节字符串中的整数值。

放弃任何空格字符,直到找到第一个非空白字符,然后采用尽可能多的字符以形成有效的整数表示并将它们转换为整数值。有效的整数值由以下部分组成:

  • (可选)加号或减号

  • 数字

参数

str

-

指向要解释的以空字符结尾的字节字符串

返回值

整数值对应str成功的内容。 如果转换后的值超出了相应返回类型的范围,则返回值未定义。 如果不能执行转换,则返回0。

#include <stdio.h>#include <stdlib.h>
 int main(void){    printf("%i\n", atoi(" -123junk"));    printf("%i\n", atoi("0"));    printf("%i\n", atoi("junk"));         // no conversion can be performed    printf("%i\n", atoi("2147483648"));   // UB: out of range of int}

输出:

-12300-2147483648

参考

  • C11标准(ISO / IEC 9899:2011):

    • 7.22.1.2 atoi,atol和atoll函数(p:341)

  • C99标准(ISO / IEC 9899:1999):

    • 7.20.1.2 atoi,atol和atoll功能(p:307)

  • C89 / C90标准(ISO / IEC 9899:1990):

    • 4.10.1.2 atoi函数

    • 4.10.1.3 atol函数

扩展内容

strtolstrtoll(C99)

将字节字符串转换为整数值(函数)

strtoul strtoull(C99)

将字节字符串转换为无符号整数值(函数)

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