从字典上比较std::strncmp(函数，对不多于两个以空值结尾的字符串的字符进行比较，并根据结果返回一个整数。
- 此函数将两个字符串和一个数字num作为参数，并比较两个字符串的最大前num个字节。
- 数最多应等于最长字符串的长度。如果将num定义为大于字符串长度，则比较将一直进行到两个字符串的null-character('\ 0')。
- 此函数按字典顺序比较两个字符串。它从每个字符串的第一个字符开始比较。如果它们彼此相等，则继续并比较每个字符串的下一个字符，依此类推。
- 比较过程将一直终止，直到到达一个终止字符串null-character或两个字符串的num个字符都匹配为止。
用法:
int strncmp(const char *str1, const char *str2, size_t count); 参数： str1 and str2: C string to be compared. count:Maximum number of characters to compare. size_t is an unsigned integral type. 返回值： Value Meaning Less than zero str1 is less than str2. Zero str1 is equal to str2. Greater than zero str1 is greater than str2.
如果任一字符串中的字符数少于计数，则在遇到第一个null时比较结束。
What does strcmp() return?
strncmp()函数在比较的基础上返回三种不同类型的整数值：
1.大于零(> 0)：如果在num字符之前str1和str2的字符不匹配并且str1字符的ASCII值大于str2字符的ASCII值，则返回正值。结果，我们可以说str1在字典上大于str2。
// C, C++ program to demonstrate
// functionality of strncmp()
#include <stdio.h>
#include <string.h>
int main()
{
// Take any two strings
char str1[10] = "aksh";
char str2[10] = "akash";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is:%d", result);
return 0;
}输出：
str1 is greater than str2 Value returned by strncmp() is:18
2.小于零(<0)：如果str1和str2的字符在num字符之前不匹配并且str1字符的ASCII值小于str2字符的ASCII值，则返回负值。结果，我们可以说str2在字典上大于str1。
// C, C++ program to demonstrate
// functionality of strncmp()
#include <stdio.h>
#include <string.h>
int main()
{
// Take any two strings
char str1[10] = "akash";
char str2[10] = "aksh";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is:%d", result);
return 0;
}输出：
str2 is greater than str1 Value returned by strncmp() is:-18
3.等于零(0)：如果str1的字符与str2的字符(最多num个字符)匹配，则此函数返回零。结果，我们不能说str1等于str2，直到num等于任一字符串的长度。
// C, C++ program to demonstrate
// functionality of strncmp()
#include <stdio.h>
#include <string.h>
int main()
{
// Take any two strings
char str1[10] = "akash";
char str2[10] = "akas";
// Compare strings using strncmp()
int result = strncmp(str1, str2, 4);
if (result == 0) {
// num is the 3rd parameter of strncmp() function
printf("str1 is equal to str2 upto num characters\n");
}
else if (result > 0)
printf("str1 is greater than str2\n");
else
printf("str2 is greater than str1\n");
printf("Value returned by strncmp() is:%d", result);
return 0;
}输出：
str1 is equal to str2 upto num characters Value returned by strncmp() is:0
注意：当字符串不同时，在两种情况下，您都会发现strncmp()函数返回的值是str1和str2中第一个不匹配字符的ASCII值之间的差。
More Examples
范例1：
// CPP program to illustrate strncmp()
#include <cstring>
#include <iostream>
void display(char* abc, char* xyz, int res, int count)
{
if (res > 0)
std::cout << xyz << " come-before " << abc;
else if (res < 0)
std::cout << abc << " come-before " << xyz;
else
std::cout << "First " << count << " characters of string "
<< abc << " and " << xyz << " are same";
}
int main()
{
char abc[] = "GeeksforGeeks";
char xyz[] = "Geeks";
int res;
res = std::strncmp(abc, xyz, 4);
display(abc, xyz, res, 4);
return 0;
}输出：
First 4 characters of string GeeksforGeeks and Geeks are same
范例2：
// CPP program to illustrate strncmp()
#include <cstring>
#include <iostream>
void display(char* abc, char* xyz, int res, int count)
{
if (res > 0)
std::cout << xyz << " come-before " << abc;
else if (res < 0)
std::cout << abc << " come-before " << xyz;
else
std::cout << "First " << count << " characters of string " <<
abc << " and " << xyz << " are same";
;
}
int main()
{
char abc[] = "GeeksforGeeks";
char xyz[] = "Geeks";
int res;
res = std::strncmp(abc, xyz, 6);
display(abc, xyz, res, 6);
return 0;
}输出：
Geeks come-before GeeksforGeeks
相关用法
注：本文由纯净天空筛选整理自 std::strncmp() in C++。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。