sprintf 的最佳实践？

Question

情况如下：

我们从使用 strcat 等 sprintf 的外部来源收到代码。像这样：

char buffer[1024];
sprintf(buffer, "Some text.");
sprintf(buffer, "%s%s", buffer, "Some more text");
sprintf(buffer, "%s%s", buffer, "again more text");

现在，这看起来很奇怪。我们都同意这看起来很奇怪。那不是我要问的。我们都知道应该用strcat，而且更直接。我问的是这可能导致的潜在问题，除了看起来很奇怪。我们运行在 RHEL6 上，使用 gcc 4.9.3。

感谢您的帮助。

Answer 1

函数声明为

int sprintf(char * restrict s, const char * restrict format, ...);

注意类型限定符restrict。

根据C标准（7.21.6.6的sprintf函数）

2 The sprintf function is equivalent to fprintf, except that the output is written into an array (specified by the argument s) rather than to a stream. A null character is written at the end of the characters written; it is not counted as part of the returned value. If copying takes place between objects that overlap, the behavior is undefined.

所以这些电话

sprintf(buffer, "%s%s", buffer, "Some more text");
sprintf(buffer, "%s%s", buffer, "again more text");

调用未定义的行为。

相反，调用可以这样写

char buffer[1024];
int offset = 0;

offset = sprintf( buffer + offset, "Some text.");
offset += sprintf( buffer + offset, "%s",  "Some more text");
sprintf( buffer + offset, "%s",  "again more text");

或

char buffer[1024];
char *p = buffer;

p += sprintf( p, "Some text.");
p += sprintf( p, "%s",  "Some more text");
sprintf( p, "%s",  "again more text");

至于限定词restrict那么一般来说就是指（6.7.3类型限定词）

8 An object that is accessed through a restrict-qualified pointer has a special association with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to that object use, directly or indirectly, the value of that particular pointer

sprintf 的最佳实践？

Best practice with sprintf?

c

standards

pointers

restrict-qualifier

asprintf