1.首先man下
ATOI(3) Linux Programmer's Manual ATOI(3)
NAME
atoi, atol,atoll, atoq - convert a string to an integer
SYNOPSIS
#include <stdlib.h>
int atoi(const char *nptr);
long atol(const char *nptr);
long long atoll(const char *nptr);
long long atoq(const char *nptr);
Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):
atoll():_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 ||
_ISOC99_SOURCE; or cc -std=c99
DESCRIPTION
The atoi() function converts the initial portion ofthe string pointed to by nptr to int. The behavior is the same as strtol(nptr, (char **) NULL, 10);except thatatoi() does not detect errors.The atol() and atoll() functions behave the sameas atoi(), except that they convert theinitial portion of the string to their return type of longor long long. atoq() is an obsolete namefor atoll().
RETURN VALUE
The converted value.
二.atoi()函數使用
1.函數功能：
把字符串轉換成整型數.
2.原型:
int atoi(const char *nptr);
3.函數說明: 參數nptr字符串，如果第一個非空格字符不存在或者不是數字也不是正負號則返回零，否則開始做類型轉換，之後檢測到非數字(包括結束符 \0) 字符時停止轉換，返回整型數。
4.頭文件: #include <stdlib.h>
5.程序例:
1>
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
int n;
char *str = "12345.67";
n = atoi(str);
printf("string = %s integer =%d\n", str, n);
return 0;
}
執行結果
string = 12345.67 integer = 12345
2>
#include <stdlib.h>
#include <stdio.h>
int main()
{
char a[] = "-100" ;
char b[] = "123" ;
int c ;
c = atoi( a ) + atoi( b ) ;
printf("c = %d\n", c) ;
return 0;
}
執行結果
c = 23